An effort to rush fresh assistance to U.S. small businesses struggling against the coronavirus outbreak stalled in Congress on Monday, as the health emergency failed to overcome partisan differences between Republicans and Democrats.

Senate Republicans, who are pressing lawmakers to agree to$250 billion in additional small business aid, chose not to bring the measure forward during a brief Senate session after Democrats reaffirmed their own demands for broader legislation.

"It's time for the Republicans to quit the political posturing by proposing bills they know will not pass either chamber and get serious and work with us towards a solution," House of Representatives Speaker Nancy Pelosi and Senate Democratic leader Chuck Schumer said in a joint statement.

The standoff began last week with a skirmish on the Senate floor, where Republicans failed to pass their narrower measure over Democratic opposition. Republicans then blocked a Democratic measure that included the same $250 billion but set aside some of the lending for community banks to aid minority-owned and rural businesses, and provided further aid to hospitals and a federal food program for the poor.

Aides to Senate Majority Leader Mitch McConnell and House Republican leader Kevin McCarthy declined to comment on the Democrats' statement.

But Republican Senator Dan Sullivan, who presided over a Monday proforma session lasting less than one minute, said the Republican bill is needed now because money for small business is beginning to run out.

"Will there be an opportunity to talk about the other programs? Yes, but a lot of us haven’t even spent any of the money at all," the Republican lawmaker told reporters.

The Democrats' latest push for broader legislation cited Republican President Donald Trump's hopes of starting to reopen the U.S. economy on May 1, by underscoring the need for additional national coronavirus testing.

"We all desire an end to the shutdown orders so we can get Americans back to work and back to normal. However, there is still not enough testing available to realistically allow that to happen," Pelosi and Schumer said. "It cannot wait."

The United States has recorded more fatalities from COVID-19 than any other country, nearly 22,000 as of Sunday evening according to a Reuters tally.

The $250 billion in small-business loans would be in addition to $349 billion already allocated by Congress in a $2.3 trillion relief measure passed last month following an earlier partisan standoff.