BAGHDAD -- Sunni militants on Sunday captured two border crossings, one along the frontier with Jordan and the other with Syria, security and military officials said, as they pressed on with their offensive in one of Iraq's most restive regions.
The fall dealt Iraq's embattled Shiite prime minister a further blow and brought the war to the doorstep of Jordan, a key ally of the United States that also borders embattled Syria to its north.
The blitz by the Islamic State of Iraq and the Levant in Iraq's vast western desert takes the al-Qaida-breakaway group closer to its dream of carving out a purist Islamic state straddling both Syria and Iraq.
Controlling the borders with Syria will also help it supply fellow fighters in Syria with weaponry looted from Iraqi warehouses, significantly reinforcing its ability to battle beleaguered Syrian government forces.
If they succeed in their quest, they could further unsettle the already volatile Middle East and serve as a magnet for Jihadists from across the world -- much like al-Qaida attracted extremists in Taliban-ruled Afghanistan.
The Iraqi officials said the militants of the Islamic State took over the Turaibil crossing with Jordan and the al-Walid crossing with Syria after government forces there pulled out.
The officials spoke on condition of anonymity because they were not authorized to speak to the media.
The capture of the two crossings follows the fall on Friday and Saturday of the towns of Qaim, Rawah, Anah and Rutba They are all in the Sunni dominated Anbar province, where the militants have since January controlled the city of Fallujah and parts of the provincial capital Ramadi.
Rutba is on the main highway from Baghdad to the two border crossing and the capture has effectively cut the Iraqi capital's main land route to Jordan. It is a key artery for passengers and goods and has been infrequently used in recent months because of deteriorating security.
Iran's supreme leader, Ayatollah Ali Khamenei, said he was opposed to any U.S. intervention in the Iraqi crisis, accusing Washington of fomenting the unrest. His comments appeared to quash recent speculation that the two rivals might cooperate in addressing the shared threat posed by the Islamic extremists.
The two crossings and the four towns are the first seized in Anbar since the Islamic State and its allies overran the city of Fallujah and parts of Ramadi. Government troops have not been able to dislodge them after months of fighting.
The capture of Rawah on the Euphrates River and the nearby town of Anah appeared to be part of a march toward a key dam in the city of Haditha, the destruction of which would damage the country's electrical grid and cause major flooding. The dam was built in 1986.
Iraqi military officials said more than 2,000 troops were quickly dispatched to the site of the Haditha dam to protect it. They spoke on condition of anonymity because they were not authorized to speak to the media.
Chief military spokesman, Lt. Gen. Qassim al-Moussawi, acknowledged the fall of the Anbar towns, saying government forces had made a tactical retreat and planned to retake them. He provided no further details. There has been no official comment on the capture of the al-Walid and Turaibil crossings.
The Islamic State and allied militants have carved out a large fiefdom along the Iraqi-Syrian border.
Al-Maliki's Shiite-dominated government has struggled to push back against the Sunni militants, who have seized large swaths of the north since taking control of the second-largest city of Mosul on June 10.
Iraq has requested U.S. airstrikes to help halt the advance, but President Barack Obama has yet to order any. He has instead called on Iraqi leaders to form a more representative government in thinly-veiled criticism of al-Maliki, and is deploying up to 300 military advisers to join some 275 troops in and around Iraq to provide security and support for the U.S. Embassy and other American interests.
In an interview with CBS' "Face the Nation" aired Sunday, Obama warned that the al-Qaida-inspired militants in Iraq could grow in power and destabilize the region.
He said Washington must remain "vigilant" but would not "play whack-a-mole and send US troops occupying various countries wherever these organizations pop up."
Iran's supreme leader, meanwhile, said he was opposed to any U.S. intervention in Iraq.
"The main dispute in Iraq is between those who want Iraq to join the U.S. camp and those who seek an independent Iraq," Khamenei, who has the final say over Iranian state policy, was quoted as saying by the IRNA state news agency, in his first reaction to the crisis. "The U.S. aims to bring its own blind followers to power."
The U.S. has long accused Iran of meddling in Iraq, including organizing and backing Shiite militias following the 2003 invasion.
Al-Maliki, who has led the country since 2006 and has not yet secured a third term after April's parliamentary elections, has increasingly turned to Iranian-backed Shiite militias and volunteers to bolster his beleaguered security forces.
Thousands of Shiite militiamen paraded through Baghdad and other cities on Saturday, brandishing a massive arsenal in a show of force that promised to ramp up sectarian tensions.
Al-Maliki has come under growing pressure to reach out to disaffected Kurds and Sunnis, with many blaming his failure to promote reconciliation for the country's worst crisis since the U.S. military withdrew in late 2011.
Grand Ayatollah Ali al-Sistani, the most respected voice for Iraq's Shiite majority, on Friday joined calls for al-Maliki to reach out to the Kurdish and Sunni minorities.
Iraq enjoyed several years of relative calm before violence spiked a year ago after al-Maliki moved to crush a Sunni protest movement against alleged discrimination and abuse at the hands of his government and security forces.
On Sunday, twin blasts by a suicide bomber and a car bomb targeted a funeral for a senior army officer in the restive Anbar province, killing eight and injuring 13, police and hospital officials said.
The attack near the provincial capital of Ramadi hit the funeral of Brig. Gen. Abdul-Majid al-Fahdawi, who was killed by a mortar shell in Qaim on the Syrian border on Friday, the day Sunni militants captured the town.
Officials said a suicide bomber first detonated his explosives at the hall where the funeral was held. Two minutes later, the car bomb went off as the mourners were fleeing, they added. The officials spoke on condition of anonymity because they were not authorized to speak to the media.
In a separate incident on Sunday, Sunni militants in control of a small northern town handed over to authorities in the northern oil city of Kirkuk the decomposing bodies of 15 Shiites, according to the city's deputy police chief Maj. Gen. Torhan Abdul-Rahman Youssef.
Residents of the town of Besher said the Shiites were hung from street lights and a water tank for days. The circumstances of their deaths were not immediately known and the residents requested anonymity for fear of reprisals.
Associated Press writer Nasser Karimi in Tehran, Iran contributed to this report.