Iraqi Prime Minister Nuri al-Maliki came under fire from US lawmakers Wednesday for the slow pace of political reconciliation and links to Iran, which they said was fuelling a wave of suicide bombings.

House lawmakers gathered to assess the threat of Al-Qaeda in Iraq and its affiliate the Islamic State of Iraq the Levant (ISIL) as a new round of bombings rocked Baghdad, killing 33 people.

Al-Qaeda is now carrying out 40 mass attacks a month, in Iraq's bloodiest eruption of violence in six years and the worse since US troops withdrew in 2011, said House Foreign Affairs Committee chairman Ed Royce.

"As head of state, while he may not be up to it, Maliki must take steps to lead Iraq to a post-sectarian era," Royce insisted.

The militants were benefiting from "the alienation" of the country's Sunni population from its Shiite dominated government, which also has strong ties with the Shiite leaders in Iran.

"Al-Qaeda has become very skilled at exploiting this sectarian rift, and Maliki's power grab has given them much ammunition," Royce said, adding that the United States had a central role to play in helping the Iraqis fight the militants.

But in a passionate outburst, his Republican colleague Representative Dana Rohrabacher questioned why the United States, which is supplying Iraq with helicopters and drones to help fight the militants, was still involved in the country.

"Why do we feel compelled that we have to go in and be in the middle of a fight between people who are murdering each other?" he asked.

"Thousands of people are losing their lives to this insanity. Why does the United States feel that we need to become part of this insanity?"

US deputy assistant secretary for Iraq Brett McGurk agreed: "The suicide bomber phenomenon, it is complete insanity."

But he said the United States, which invaded the country in 2003 to topple late dictator Saddam Hussein, had strategic interests to protect in the Middle East nation.

"In Iraq whether you like it or not, oil, Al-Qaeda, Iran , vital US interests are at stake," he said.

And he insisted Maliki had made changes, particularly in trying to reconcile Sunni and Shiites, since his visit to Washington in November during which he "got a very direct message" in his two-hour meeting with President Barack Obama.

Maliki was told of "the need for a wholistic strategy to defeat ISIL and enlisting the Sunnis into the fight. At the local level we've seen some fairly dramatic and significant changes," McGurk said.

The committee's ranking Democrat Eliot Engel said however he believed Maliki "just came to listen, but really didn't come to put his head together with us and help solve the problem."