WASHINGTON - Bipartisan Senate negotiators reached agreement Tuesday on a $4.5 billion emergency spending bill for the U.S.-Mexico border, amid urgent warnings that agencies will run out of money at the end of this month to deal with the surge of migrants from Central America.

The deal is expected to pass the Senate Appropriations Committee on Wednesday and the full Senate next week. But the deal does not include the House, where members of the Congressional Hispanic Caucus have strongly opposed elements of the administration's spending request, leaving the ultimate resolution uncertain.

The Senate deal includes $2.9 billion for the Department of Health and Human Services to care for unaccompanied migrant children, with the remainder of the money split between the departments of Justice, Homeland Security and Defense, according to a senior congressional aide. The aide spoke on the condition of anonymity to disclose details before the agreement is unveiled at Wednesday's meeting of the Senate Appropriations Committee.

Administration officials have repeatedly pressed Congress for more resources to deal with the dramatic increase in the number of migrants being apprehended at the southern border, which has reached its highest levels in more than a dozen years. Earlier this month the Trump administration began canceling English classes, recreational programs and legal aid for unaccompanied minors at federal migrant shelters, citing budgetary pressures.

In May, more than 144,000 migrants were taken into custody at the U.S.-Mexico border, according to U.S. Customs and Border Protection data. Preliminary figures for June - a time when President Donald Trump threatened to impose tariffs on all goods from Mexico if it didn't step up immigration enforcement on its end - show the number of migrant families at the border has been falling, although officials have cautioned that it is premature to draw any conclusions on migration levels for this month.

On Monday night, Trump announced in a tweet that immigration agents would soon begin making mass arrests of immigrants who had made their way into the United States.

The deal was struck by Appropriations Committee Chairman Richard Shelby, R-Ala., and the committee's ranking Democrat, Patrick Leahy of Vermont. It matches the $4.5 billion the administration requested from Congress on May 1, although the administration had subsequently increased the request, informally, to $4.9 billion.

Democrats had sought various restrictions and reporting requirements on how the money could be used, which Republicans and the administration largely opposed. It was not immediately clear how those disputes were resolved.

Negotiations continue in the House, which may vote on its own version of a border spending bill next week. That would leave Congress a matter of days to reach an agreement on a final deal before the month's end, when the administration has warned that money will run dry and more services would be cut.

But House Democrats are also navigating their own internal divisions on how to advance the administration's funding request, with members of the Congressional Hispanic Caucus demanding additional safeguards to ensure the money is spent on legitimate humanitarian purposes. "We're just getting the information we need to make an assessment of the legislation," the group's chairman, Rep. Joaquin Castro, D-Texas, said Tuesday evening. "We very much want to help alleviate the humanitarian situation at the border. Yet all DHS funding requests must now be scrutinized in light of President Trump's declaration of mass immigration raids by ICE starting next week."

In recent days Republicans have repeatedly attacked Democrats, accusing them of failing to cooperate on an urgent humanitarian and national security issue.

"The president seemed to me to be getting more cooperation from Mexico than he is from congressional Democrats on dealing with the crisis at the border," Senate Majority Leader Mitch McConnell, R-Ky., said Tuesday. "Let me say again, this is not wall funding. This is a humanitarian crisis of gargantuan proportions. It needs to be dealt with."

This article was written by Erica Werner and Seung Min Kim, reporters for The Washington Post.