Iraqis burn the American flag in the southern city of Basra during a protest on Monday. Hussein Faleh/AFP

Iraq's government warned that its relations with the United States were at risk after deadly American air strikes against a pro-Iran group sparked anger on the streets, with protesters torching US flags.

US hits pro-Iran group with deadly strikes in Iraq Syria

Baghdad said it would summon the US ambassador while Washington responded by accusing Iraqi authorities of having failed to "protect" US interests.

At least 25 fighters were killed in Sunday night's attacks, which saw US planes hit several bases belonging to the Hezbollah Brigades, one of the most radical factions of Hashed Al Shaabi, a Tehran-backed Iraqi paramilitary coalition.

Iraqis wave Hashed Al Shaabi armed network flags in the southern city of Basra on Monday. Hussein Faleh/AFP

The attacks came as Iraq is caught up in mounting tensions between its allies Tehran and Washington while it also grapples with huge street protests against corruption and Iran's growing political influence in the country.

The strikes "killed 25 and wounded 51, including commanders and fighters, and the toll could yet rise," said the Hashed, which holds major sway in Iraq.

Victims were still being pulled from the rubble of bases near Al-Qaim, an Iraqi district bordering Syria, on Monday, it said.

The Hezbollah Brigades said they will hold a mass funeral ceremony on Tuesday in Baghdad near the high-security Green Zone, where the US embassy is located.

Protesters stage a sit-in on barriers at a bridge leading to the heavily fortified Green Zone in Baghdad on Monday. AP

Iraq's government, acting in a caretaker capacity following the resignation of prime minister Adel Abdel Mahdi in the face of street protests, denounced the strikes and warned they could affect ties with Washington.

"American forces acted on their political priorities, not those of the Iraqis," a statement said, adding that such strikes "violate the sovereignty of Iraq".

The attacks "force Iraq to review its relations and its security, political and legal framework to protect its sovereignty", the government added.

The warning came as demonstrators torched US flags in the Shiite-dominated southern cities of Basra and Najaf as well as in Kirkuk, north of Baghdad, while lawmakers called for US troops to be booted out of Iraq.

Outgoing premier Abdel Mahdi said it is up to parliament to determine the next move, according to a video released by his office.

"We will see what parliament will decide. We are only a caretaker government," he said.