Volunteers have joined the Iraqi army to defend the country from predominantly Sunni militants. Thaier Al-Sudani/Reuters The United States needs Iran's involvement to prevent a collapse of the government in Iraq and should open talks toward that end, U.S. Senator Lindsey Graham said on Sunday, describing the step as unattractive but perhaps unavoidable.

"We are probably going to need their help to hold Baghdad," from takeover by the Islamic State in Iraq and the Levant (ISIL), the Sunni Muslim militant group that has seized control over northern Iraqi cities and is approaching the nation's capital, Graham, a South Carolina Republican, said on CBS' "Face the Nation."

"The Iranians have an interest. They have Shia populations to protect. We need a dialogue of some kind," to help stabilize Iraq but also to set limits to ensure Iran does not use the situation to seize territory, he said.

The advance of ISIL fighters on Baghdad slowed on Sunday as the government of Prime Minister Nuri al-Malikitried to rally its forces and stave off a civil war.

Still, a suicide bombing in Baghdad and fierce fighting in the northern town of Tal Afar highlighted the country's slip into sectarian violence between a Sunni minority and the Shi'ite-dominated government.

Graham, a member of the Senate Armed Services committee, is a leading Republican voice on military policy and has taken a hard line in the past towards Iran. He has suggested that military action against that country might beneeded to stop its development of nuclear weapons.

He also opposed the 2011 withdrawal of the final U.S. troops from Iraq, arguing that an outside force would beneeded to help a reconstituted Iraqi army keep order.

The United States and Iraq had discussed leaving a U.S. force in place, but were unable to come to terms. With the country now at risk of fracturing, Graham's comments were part of a flurry of Republican criticism on Sunday of the Obama administration's response to the crisis.

Obama has ruled out the use of U.S. ground troops, and said any air support or other assistance was conditional on Maliki trying to overcome divisions between Sunnis and Shi'ites that have widened under his rule.

"It is too late to have long political reconciliation meetings that will last weeks or months," House Intelligence Committee Chairman Mike Rogers, a Michigan Republican, said on "Fox News Sunday." "You have an al Qaeda army on the move."

Rogers said the administration should organize neighboring Arab states in a joint response, and support that withU.S. intelligence, air power, and other assistance. He said the threat was not just regional, but of ISIL establishing a safe haven for itself, and using that to plan attacks against targets in the United States or Europe.

Graham last week said American air strikes in Iraq will be needed to halt the advance of militants.

His comments about Iran broach an even more sensitive topic - putting the United States in potential collaboration with a country it suspects of developing nuclear weapons and supporting its own militant groups in places like Lebanon.

Iranian officials, closely allied with Maliki and watchful over the Shi'ite population centered in southern Iraq, have also been alarmed at the sudden seizure of territory by the ISIL.