(CNN) The political battle over Zika funding intensified Tuesday as congressional Democrats and the White House amped up pressure on Republicans to pass money aimed at combating the dangerous virus that is spreading north to the United States.

"This is an emergency if there ever were an emergency," said Harry Reid who blamed GOP senators for a "continual pattern of constant Republican gridlock" that the Senate minority leader said was blocking swift passage of the money.

"The Senate should not leave this week without addressing the legislation that deals with Zika," the Nevada Democrat declared.

Late on Tuesday two top White House officials -- National Security Advisor Susan Rice and Budget Chief Shaun Donovan -- sent letters to House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell complaining that 64 days after the administration asked for $1.9 billion, "Congress has not acted." The letters also warned the public health threat has increased, noting that the Centers for Disease Control and Prevention is reporting 891 confirmed cases of Zika in the United States and U.S. territories, including 81 pregnant women as of April 20.

Last week, bipartisan Senate negotiators reported they were narrowing in on a deal to provide a little more than half of President Barack Obama's request. They were upbeat about getting a deal soon, even though there were still many policy and procedural hurdles to clear.

One of the negotiators, Sen. Patty Murray of Washington, who is also a member of the Democratic leadership, even praised Republicans for working in "good faith" to reach an agreement.

But when Democrats huddled in their weekly policy lunch in the Capitol Tuesday rank-and-file senators pushed back against the emerging deal and pressed their leaders to go back the table and insist Republicans approve Obama's full request, according to multiple sources familiar with the discussion. Those Democrats argued that any deal eventually cut with House Republicans would likely pare back Obama's original request even further so Senate Democrats should fight to preserve as much of it as they can in the Senate bill now.

"We cannot wait to act. With the mosquito season coming here and families wondering what is being done to protect them," said Murray in a notably tougher political attack than a week ago. "Today we are here to send a very clear message to our colleagues across the aisle. There is no more time to wait. We need to get an emergency funding agreement through the Senate this week."

Senate Republican leaders, who spoke to reporters shortly before the Democrats did, agreed that the virus was a real public health threat, and one after another told reporters they were working across the aisle to cut a deal. They also pointed out that the administration was already using $600 million in Ebola funding Congress approved last year to deal with Zika.

"We all are very much aware that this is a serious crisis," said McConnell, a Republican from Kentucky. "We'll be working with the administration, with the Democrats."

Democrats tried to tie GOP inaction on Zika to the decision by Republican Senate leaders not to confirm Judge Merrick Garland to the Supreme Court or approve money for the Flint, Michigan water crisis.

Sen. Chuck Schumer of New York, who is in line to the next Democratic leader, blamed a group of about 15 Senate Republicans for blocking Senate action.

"You have a hard right group that says we don't want to spend money on anything. And it paralyzes them even when there's a national emergency. So Republicans are tied in a knot. They're not doing their jobs," Schumer said.

Sen Dick Durbin of Illinois, the assistant Democratic leader, jabbed at the GOP for not moving ahead of an upcoming congressional break, saying, "mosquitoes are not going to be on recess next week."

The effort to increase pressure on Republicans will continue Wednesday, with Reid and House Minority Leader Nancy Pelosi slated to appear at a joint news conference to push for quick action on Zika.

Negotiators are grappling with a several issues besides just the overall cost. For instance, Democrats want the funding designated "emergency" so it won't count against the caps of last year's budget deal. Most Republicans oppose that idea although some -- including Lindsey Graham of South Carolina who is one of the principal negotiators -- are open to it.

House Majority Leader Kevin McCarthy said Tuesday the administration could use some of the leftover money at existing accounts to combat Ebola to address immediate needs with Zika, saying, "there is enough money there, especially to deal with this year."

But in the letter from White House officials they stressed that that money was "insufficient." They also said that without additional money approved by the summer months "the Nation's efforts to comprehensively respond to the disease will be severely undermined" citing that state efforts to mitigate mosquito abatement might need to be stopped, vaccine development would be stalled, and the administration won't be able to follow up on existing cases to determine the full health impacts of the virus.

Democrats and the White House also want the money to move through Congress as a stand-alone supplemental bill. House Democrats introduced their own bill Monday, but Republicans oppose that and want to tack in onto one of the yearly appropriations bills working through the Congress now. Democrats argue that will slow passage and complicate getting the money out quickly.

In the letter from the White House delivered Tuesday, Donovan and Rice reiterated their desire for a stand-alone bill, and urged Congress to approve the full $1.9 billion request before the Memorial Day recess in late May.

Earlier in the day McCarthy made it clear the House GOP leaders plan to take up the issue as part of the annual debate on spending bills for federal agencies, not separately.

"I do believe the best place to deal with this is in the appropriations process," McCarthy told reporters Tuesday, saying he is still looking for answers to some of the detailed questions GOP members sent the administration about how the Zika funds would be spent.

Democrats are also pushing to add funds for Puerto Rico's health care system because the U.S. territory already has about 500 reported cases of Zika virus.

Another question is whether any of the Ebola money that is for the fight against Zika should be replenished.

"We've spent a lot of time since the (President's) proposal, but especially in the last ten days trying to find the right number and the right way to deal with this and intend to," said Sen. Roy Blunt, a Republican of Missouri, who chairs the health subcommittee of the Appropriations Committee.

Republicans on the House Appropriations Committee are doing their own assessment of what resources are needed for federal agencies to combat the Zika virus, and may present their own package once they get more information from the Administration on the scope of the various programs.