Democrat dissenters have voiced doubts over a Republican commitment to negotiate an immigration deal that proved pivotal in ending a three-day government shutdown.

California senator Kamala Harris suggested it was “foolhardy” to take Republican Senate leader Mitch McConnell on his word after he pledged to take up the issue of protections for young immigrants to secure a short-term federal funding deal.

Mr McConnell said his party had “come to an agreement” to negotiate with Democrats on the issue, which had been a sticking point throughout efforts to end the shutdown.

The Democratic Senate leadership subsequently agreed to back a stopgap spending bill to finance the government for three weeks, despite no concrete immigration concessions being placed on the table. The House of Representatives later quickly approved the compromise.

Democrats had wanted protections from deportation for so-called “Dreamers”, more than 700,000 young undocumented immigrants brought to the US as children. But Republicans insisted no agreement was possible while government services were closed.

Senate minority leader Chuck Schumer said he was trusting the pledge of his Republican counterpart to allow a “free and open debate” on immigration.

But Democrats who voted against the bill and members of the party’s liberal base criticised the agreement, some suggesting Mr Schumer and others had “caved”, echoing the words of President Donald Trump.

Ms Harris said: “The Majority Leader’s comments fell far short of the ironclad guarantee I needed to support a stopgap spending bill. I refuse to put the lives of nearly 700,000 young people in the hands of someone who has repeatedly gone back on his word.”

She suggested it was “foolhardy to believe” Mr McConnell “had made any commitment whatsoever”.

Ms Harris is tipped to run to the Democratic election candidate in 2020, as were several other senators who voted against the bill, which passed 81 to 18.

Another California senator, Dianne Feinstein, said she was “very disappointed” in the deal as there was no guarantee the Republicans would help to protect Dreamers.

Democratic congressman Luis Gutierrez also criticised by his party’s senators, saying: "They caved. They blinked. That’s what they do.”

Other senators voted against the bill still voiced optimism that Mr McConnell would stay true to his word.

"McConnell made a pledge in front of the world," said Ohio's Sherrod Brown, adding he was "counting on him" to keep to his promise.