Sunni Muslim Saudi Arabia and Shi'ite Iran had been about to "reach a breakthrough over the situation in Iraq and the region", Abdul Mahdi said.

Iranian-backed militia and US troops fought side by side during Iraq's 2014-17 war against Islamic State. Iraqi militia leader Abu Mahdi al-Muhandis was also killed in Friday's strike.

Sunday's parliamentary resolution was passed by overwhelmingly Shi'ite lawmakers, as the special session was boycotted by most Sunni Muslim and Kurdish lawmakers.

One Sunni member of parliament said that both groups feared that kicking out US-led forces would leave Iraq vulnerable to insurgents, undermine security and heighten the power of Iranian-backed Shi'ite militias.

In Iran on Sunday, hundreds of thousands of mourners, many chanting, beating their chests and wailing in grief, paid their respects after Soleimani's body was returned to the city of Ahvaz.

In a series of tweets posted on Saturday, Trump wrote that Iran "is talking very boldly about targeting certain USA assets" in revenge for Soleimani's death. He said the US had "targeted 52 Iranian sites" and that some were "at a very high level & important to Iran & the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD".

"Killing General Soleimani seems to have deterred and de-escalated nothing," The New York Times said Sunday in an editorial, which added that targeting cultural sites is considered a war crime. "Otherwise, why would the State Department have needed to advise all Americans to leave Iraq?"

In remarks to Fox News on Sunday, Pompeo said Trump had not threatened to target Iranian cultural sites.

Leading Democratic candidates for president in 2020 at first were cautious about criticizing Trump, but that changed on Sunday, with US Senator Elizabeth Warren saying Trump ordered the attack to detract attention from his recent impeachment and that the job of the president is "not to move us to the edge of war".

Senator Bernie Sanders of Vermont tweeted Sunday: "Congress must reassert its constitutional responsibility over war. The Senate and House must vote to immediately defund unauthorized military action against Iran."

Jon B. Alterman, a senior vice-president of the Center for Strategic & International Studies in Washington, said that Iran will respond, forcing itself to the forefront of US foreign policy considerations for years to come and drawing the United States into precisely the sort of battles the Pentagon has been trying to escape for more than a decade.

Over the weekend, antiwar protests took place in more than 70 US cities, according to Agence France-Presse. In Washington, protesters gathered outside the White House and at the nearby Trump International Hotel.

In the US, war fears led to a sharp rise in searches about the Selective Service System, which identifies potential prospects in the event of a military draft.

Google searches for the question, "Is there going to be a draft?"rose 900 percent in a day, The Washington Post reported.

The Selective Service System warned against misleading reports and rumors.

"Due to the spread of misinformation, our website is experiencing high traffic volumes at this time," the Selective Service System tweeted. "If you are attempting to register or verify registration, please check back later today as we are working to resolve this issue."

Zhao Huanxin in Washington and Reuters contributed to this story.