The threat of a US government shutdown surged on Friday, as the US Senate rejected a short-term funding bill to keep federal agencies operating after September 30 and then left town for a week-long break.

The lawmakers voted 44-48 to defeat a stopgap spending bill that would have kept federal agencies operating at current funding levels through November 21. The measure faced near universal opposition from Democrats, who demanded increased healthcare funding.

Republicans said they could vote again on September 29, just a day before funding is due to expire, when senators return from a break.

Senate Majority Leader John Thune blamed Democrats for increasing the chances of a shutdown. "Eventually, it's going to be an up or down vote on whether they want to keep the government open," he said.

Democrats had demanded additional funding for healthcare subsidies under the Affordable Care Act and the restoration of funding cut from the Medicaid healthcare program for lower-income Americans. But that effort failed 47-45.

Congress has struggled to pass spending legislation in recent years due to rising partisan tensions, repeatedly raising the threat of a shutdown that would leave government workers unpaid and a wide range of services disrupted.

The temporary spending bill included $88 million to protect lawmakers, executive branch officials and the Supreme Court in the aftermath of conservative activist Charlie Kirk's assassination.

Only 43 Republicans and one Democrat, Senator John Fetterman, voted for it, far short of the 60 votes needed to pass the Senate. Two Republicans, Senators Lisa Murkowski and Rand Paul, joined other Democrats and independents in opposition. Republicans were also plagued by absences, with eight members not voting.

The annual funding debate covers only about one-quarter of the federal government's $7 trillion budget, which also includes mandatory programs such as Social Security and Medicare, as well as payments on the nation's $37.5 trillion debt.

The same stopgap bill passed the Republican-controlled U.S. House of Representatives by a vote of 217-212. In a move to pressure Senate Democrats, House Republican leaders said they would not return until after Oct. 1.

"If there was ever a sign that the Republicans wanted a shutdown, that's it," Senate Democratic leader Chuck Schumer said.