WASHINGTON — Democrats say top GOP lawmakers are proposing to partially fund President Barack Obama's request for money to fight the Zika virus.

The $1.1 billion measure circulating Wednesday comes in advance of an appropriations panel meeting Thursday and was being worked on with Democrats in hopes of winning their support. The measure has not been finalized and is part of continuing negotiations. The money would be used to try to slow the spread of the Zika virus and develop a vaccine against it.

Top Appropriations Committee Democrat Barbara Mikulski of Maryland said the issue is “in play” for a Thursday panel vote.

“I am very hopeful they are coming to the table and we'll see what happens in the next 24 hours,” said Sen. Patty Murray, D-Wash.

“I think we're working toward something that could produce results even this week,” said Sen. Roy Blunt, R-Mo., who has responsibility for a panel that oversees the bulk of the request.

Republicans controlling Congress have come under pressure to respond to Obama's $1.9 billion request to combat Zika, which can cause grave birth defects and is expected to worsen in coming months.

Republicans succeeded in forcing the administration to shift almost $600 million of previously-approved funds for immediate action against Zika.

But the White House and its Democratic allies, who say more money is needed now, have turned up the heat on Republicans, who are responsible for shepherding the Obama request since they are in control of both sides of Capitol Hill. They are demanding that the Zika-fighting money be added to the budget as an “emergency supplemental,” which means it would be added to December's spending measure for the ongoing fiscal year.

It's not clear how GOP leaders might try to advance the measure, though it's unlikely to advance on its own. The Appropriations panel has two measures before it Thursday, and there is also a widely-backed measure funding energy and water projects pending on the Senate floor.

A key consideration for lawmakers is making sure that Zika money is approved before Congress leaves in mid-July for a seven-week break.