The US Senate voted Thursday to restrain President Donald Trump from attacking Iran, with eight members of his Republican Party bucking their leadership to agree. The resolution, which requires Trump to seek explicit authorization from Congress before further hostilities with Iran, passed in similar form in the Democratic-led House of Representatives.

But it faces a near-certain veto from Trump after it goes back through the House. The resolution passed 55-45, with eight Republicans joining the Democrats. The resolution asks the president to go to Congress for explicit authorization to attack Iran, but makes an exception for defending against an "imminent" threat.

Trump is expected to veto the legislation, he warned the Senate Wednesday to vote it down and not limit his policy choices. "It is very important for our Country's SECURITY that the United States Senate not vote for the Iran War Powers Resolution," he tweeted.

"We are doing very well with Iran and this is not the time to show weakness. If my hands were tied, Iran would have a field day. Sends a very bad signal. The Democrats are only doing this as an attempt to embarrass the Republican Party."

In January the Democrat-controlled House of Representatives passed its own version of the law, after Trump's order to kill Iranian commander Qasem Soleimani and retaliatory missile strikes by Tehran dramatically escalated tensions and raised fears of a devastating war between the two foes.

Democratic Senator Tim Kaine, the sponsor of the Senate resolution, said it aimed at preventing unilateral war. "Congress has got to reassert our constitutional role in matters of war and peace," he said. The two chambers' versions will have to be reconciled before being sent to the White House, which could all take place by the end of February.