Speaker Nancy Pelosi (D-Calif.) and Senate Minority Leader Charles Schumer (D-N.Y.) on Thursday panned an emerging GOP proposal for a coronavirus relief package as falling "very short," while ruling out any short-term extension of aid that's expiring in the next few days.

Treasury Secretary Steven Mnuchin said that Senate Republicans and the White House reached a "fundamental agreement" on a coronavirus aid bill. But the text of the agreement has yet to be released as of early Thursday afternoon.

The emerging proposal, which Senate Republicans and the White House have been negotiating with each other all week, is expected to be about $1 trillion. It's expected to include a second round of stimulus checks for individuals making up to $75,000 annually, as well as replace the $600 weekly boost to unemployment insurance with a roughly 70 percent match of a worker's wages before they were laid off. It is also expected to include $105 billion for schools to help them reopen and $16 billion in funds for coronavirus testing efforts.

Pelosi and Schumer blasted the proposal as insufficient and lacking in key areas prioritized by Democrats, including food assistance, helping people pay rent and avoid evictions, funding for state and local governments, providing hazard pay to essential workers and funding for administering elections this fall during the pandemic.

"What we have seen so far falls very short of the challenge that we face in order to defeat the virus and to open our schools and to open our economy," Pelosi, flanked by Schumer, said at a news conference in the Capitol.

"Republicans need to pull their head out of the sand, get their act together, sit down with Speaker Pelosi and me, and start negotiating a real package," Schumer said.

The weekly $600 federal supplement to unemployment insurance established by a March coronavirus relief law is set to expire this weekend due to a quirk in state unemployment insurance systems that mostly pay out in cycles ending on Saturdays.

Some Senate Republicans briefly floated the idea on Wednesday of temporarily extending the unemployment insurance on a short-term basis while the negotiations are likely to stretch on for at least another couple weeks. But the idea was ultimately scrapped by GOP leaders and the White House hours later.

Pelosi and Schumer also rejected the idea of a short-term extension.

"We cannot piecemeal this," Pelosi said, while Schumer said "we have to address it as a totality."

House Democrats passed a $3 trillion coronavirus relief package in May that would, among other provisions, provide nearly $1 trillion for state and local governments, extend the $600 weekly unemployment insurance supplement through January, and allot a second round of stimulus checks of up to $1,200 for individuals making up to $75,000.

Senate Republicans have rejected that bill. But they have yet to unveil their own bill as a starting point in the coming negotiations with Democrats, with Republicans struggling to reach a deal this week over days of talks with Mnuchin and White House chief of staff Mark Meadows.

Schumer expressed pessimism that a bipartisan deal could be reached by the end of next week.

"I hope so, but they're so divided," Schumer said of Republicans. "At the same time that they know that the president has no leadership, they're afraid to buck him on anything."