The House of Representatives Building and the East Portico of the US Capitol. Photo: Flickr.

Republican leaders of the US House of Representatives unexpectedly canceled a vote on Thursday on a resolution seeking to end the Iran war unless President Donald Trump obtains Congress’ authorization, two days after a similar measure advanced in the US Senate.

The vote had been scheduled to take place late Thursday afternoon, just before lawmakers left Washington for their Memorial Day recess.

The House had blocked three previous war powers resolutions in close votes earlier this year, with near-unanimous support from Republicans, underscoring the strong backing for the Iran war and the president within his party.

But the margins had become increasingly narrow – the last resolution failed on a tie vote – as weeks passed since the US and Israel began striking Iran on February 28. Thursday’s measure looked likely to pass, given expected defections by a handful of Republicans and the absences of others.

“We had the votes without question, and they knew it,” Representative Gregory Meeks, the top Democrat on the House Foreign Affairs Committee, told reporters after the vote was canceled.

He said the chamber’s Republican leaders had delayed the vote until early June, after the Memorial Day recess.

Democrats, and a few Republicans, have called on Trump ​to come to Congress for authorization to use military force, noting that the US Constitution says that Congress, ​not the president, can declare war. They have expressed concerns that Trump may have entered the country into a long conflict without setting out a clear strategy.

Most Republicans, and the White House, say Trump’s actions are legal and within his rights as commander-in-chief to protect the US by ordering limited military operations to stop imminent threats.

Republicans control narrow majorities in both the House and Senate.

On Tuesday, the Senate advanced a separate, but similar, war powers resolution, in a rare rebuke of Trump. That procedural vote on whether to advance the measure for further votes was 50 to 47, as four of Trump’s fellow Republicans voted with every Senate Democrat but one in favor. Three Republicans missed that vote.