BAGHDAD — The last Iraqi security forces fled the provincial capital of Ramadi on Sunday, as the city fell completely to the militants of the Islamic State, who ransacked the provincial military headquarters, seizing a large store of weapons, and killed people loyal to the government, according to security officials and tribal leaders.
The fall of Ramadi to the Islamic State, despite intensified American airstrikes in recent weeks in a bid to save the city, represented the biggest victory so far this year for the extremist group, which has declared a caliphate, or Islamic state, in the vast areas of Syria and Iraq that it controls. The fall of Ramadi also laid bare the failed strategy of the Iraqi government, which had announced last month a new offensive to retake Anbar Province, a vast desert region in the west of which Ramadi is the capital.
“The city has fallen,” said Muhannad Haimour, the spokesman for Anbar’s governor. Mr. Haimour said that at least 500 civilians and security personnel had been killed over the last two days in and around Ramadi, either from fighting or executions. Among the dead, he said, was the 3-year-old daughter of a soldier.
“Men, women, kids and fighters’ bodies are scattered on the ground,” said Sheikh Rafi al-Fahdawi, a tribal leader from Ramadi, who was in Baghdad on Sunday and whose men had been resisting the Islamic State, also known as ISIS or ISIL.
He also said, “All security forces and tribal leaders have either retreated or been killed in battle. It is a big loss.”
The loss of Ramadi came a day after the Pentagon said Special Operations Forces, flying in helicopters that took off from Iraq, carried out a raid in eastern Syria that resulted in the death of an Islamic State leader and the capture of his wife, along with a trove of materials American officials hope will yield important intelligence on the group.
American officials have also insisted recently that the Islamic State is on the defensive in Iraq, noting that the group has lost territory in Salahuddin Province and in some other areas in northern Iraq near the border with the autonomous Kurdish region. Yet the fall of Ramadi shows that the group is still capable of carrying out effective offensive operations.
Anbar Province holds painful historical import for the United States as the place where nearly 1,300 soldiers and marines died after the American invasion of 2003. Since the beginning of 2014, months before the fall of Mosul and the start of the American air campaign against Islamic State, the United States has been working with the Iraqi government to push back the extremist group in Anbar, sending vast supplies of weapons and ammunition and, more recently, training Sunni tribal fighters at an airbase in the province.
With defeat looming in Ramadi on Sunday afternoon, the Anbar Provincial Council met in Baghdad and voted to ask Prime Minister Haider al-Abadi to send Shiite irregulars to rescue Anbar, a largely Sunni province. In response, Mr. Abadi issued a statement calling for the militias, known as the Popular Mobilization Forces and including several powerful Shiite forces supported by Iran, to be ready to fight in Anbar. Some of the Shiite irregular units, which were formed last summer after Shiite clerics put out a call to arms, are more firmly under the command of the government, while others answer to Iran.
The involvement of the militias in Anbar had been opposed by the United States, which leads an international coalition that has been carrying out airstrikes in support of Iraqi forces. American officials had worried the militias could inflame sectarian tensions in the province and ultimately make it harder to pacify.
As they considered asking for the assistance of the militias, Anbar officials met over the weekend with the American ambassador to Iraq, Stuart E. Jones, to ascertain the United States position on the issue. According to officials, Mr. Jones told the Anbar delegation that the United States would continue its air campaign, provided that the militias were under the command of Mr. Abadi, and not Iranian advisers, and that the militias were properly organized so as to avoid becoming casualties of American bombing runs.
At the outset of an offensive to liberate Tikrit, in Salahuddin Province, in March, the Iranian-backed militias took the lead on the ground, and American warplanes stayed away. Once those militias stalled, Mr. Abadi ordered them to retreat, which was followed by American airstrikes and an advance by Iraqi security forces, and the liberation of Tikrit.
In the wake of that victory, Mr. Abadi promised a new effort in Anbar, a campaign that was supposed to be led by the Iraqi security forces and supported by American airstrikes, with Iran and its militias on the sidelines. A key component of that strategy was to arm local Sunni tribesmen to do the fighting, but that plan never materialized in large numbers, partly because of resistance by powerful Shiite political leaders in Baghdad.
The deterioration of Anbar over the last month underscored the ineffectiveness of the Iraqi Army, which is being trained by American military advisers, and raised questions about the United States strategy to defeat the Islamic State. At the same time, now that the militias are being called upon, the collapse of Ramadi has demonstrated again the influence of Iran, even if its advisers are unlikely to be on the ground in Anbar, as they were during the operation in Tikrit.
The Islamic State, which has held areas around Ramadi for nearly a year and a half, began an offensive on the city late Thursday night, and on Friday afternoon captured the provincial government headquarters.
Mr. Abadi on Friday promised to send reinforcements to the city, but ultimately only a couple hundred soldiers arrived from Baghdad to help resist in one of the last contested neighborhoods in the city, according to a security official in Anbar.
American officials in Washington downplayed the situation Friday, saying it was similar to the up-and-down fighting that had been continuing there since the beginning of last year.
Yet the Islamic State was able to consolidate its hold of the city over the weekend, and on Sunday seized one of the last government redoubts — the local operations command center. The remaining officers and soldiers had fled, and one of them reached by telephone Sunday afternoon said they were stuck in a convoy southwest of Ramadi, with Islamic State militants closing in from four sides.
Another soldier who had been stationed at the Anbar Operations Command headquarters said the forces left behind a huge cache of heavy weapons that had recently been sent by Baghdad, including rocket-propelled grenades and heavy machine guns. The weapons had been supplied by both the United States and Russia.
“ISIS is gaining more weapons, and the battle will be harder in the future,” said the soldier, who declined to give his name because he feared for his life.
Shiite militia leaders on Sunday, who had mostly watched the collapse of Anbar from afar, were scrambling to mobilize their men.
Mueen al-Kadhumi, a leader in the Popular Mobilization Forces and a member of the Badr Organization, a longstanding militia with ties to Iran, said, “We have recalled all off-duty fighters to join their units as soon as possible to participate in the upcoming battle for Anbar.”
Pentagon officials said Sunday that it was premature to declare that Ramadi had fallen.
“We’re continuing to monitor reports of tough fighting in Ramadi and the situation remains fluid and contested,” said Col. Steven H. Warren, a Defense Department spokesman.
Coalition warplanes carried out more attacks on Islamic State targets in Iraq, with seven airstrikes on militant positions in or near Ramadi over the weekend, according to official statements. But the advance by Islamic State fighters was evidence again that American air power alone cannot hold territory for the Baghdad government, nor dislodge militants, without an effective Iraqi force on the ground to battle the Islamic State fighters.
As the Islamic State sealed its advance into Ramadi, the wife of the militant organization’s senior financial officer remained in American custody in Iraq on Sunday. The wife, Umm Sayyaf, was captured by Delta Force commandos during the Saturday raid into Syria that killed her husband, Abu Sayyaf, and about a dozen militant fighters.
One senior American official, who spoke on the condition of anonymity to discuss the ongoing investigation, said Umm Sayyaf “was more than just her husband’s right-hand man and partner. She was likely involved in details about the hostage-taking, and how that worked.”
This official acknowledged that Abu Sayyaf’s death likely would present only a minor disruption in the Islamic State’s broader financial operations, which include black-market sales of petroleum products to raise cash.