WASHINGTON (AP) — Congress is at a standoff over a $4.6 billion aid package for the southern border as House Democrats say a Senate-passed measure doesn't go far enough to care for thousands of migrant families and children.

Speaker Nancy Pelosi is considering a fresh vote Thursday.

"We're not making predictions, threats, or anything else. We're just saying this is a moral imperative for us to do the right thing for the children," Pelosi said Thursday morning.

Democrats want to add more protections for the children — including medical and hygiene standards at facilities, and a requirement that any death of a minor be reported within 24 hours. Democratic leaders will convene early Thursday and Pelosi's spokesman says they plan to push the amended measure through the House quickly. The White House said it opposes changes planned by the Democrats.

It's a risky stalemate over a border crisis that has captured global attention amid unsettling reports of gruesome conditions at federal facilities and the deaths of migrants and children. The funding is urgently needed to prevent the humanitarian emergency on the U.S.-Mexico border from worsening. Money runs out in a matter of days.

The GOP-led Senate on Wednesday passed a bipartisan $4.6 billion measure on a sweeping 84-8 vote. Approval came less than 24 hours after the Democratic-controlled House approved a similar measure backed by liberals. The House bill, which contained tougher requirements for how detained children must be treated, faced a White House veto threat and was easily rejected by the Senate.

Pelosi called President Donald Trump before he departed for the G-20 Summit in Osaka, Japan, with an appeal to make changes. Trump seemed open, but it's unclear if the Senate will accept any amendments without assurances from the White House that Trump will sign the measure into law. Both chambers are racing the clock to come to an agreement before leaving town for a weeklong recess.

Trump said passing the legislation was urgent. "We are moving along very well with a bipartisan bill in the Senate," he said. "It's very far along and I believe the House is also going to also be getting together with the Senate to get something done. It's humanitarian aid. It's very important."

Republicans and the White House far prefer the Senate measure, but Pelosi is pressing for quick resolution — promising that Democrats won't knuckle under. Asked ahead of voting if the House would pass the Senate bill and send it to Trump, Pelosi said, "No."

Failure to act before the recess could bring a swift political rebuke and accusations of ignoring the plight of innocent immigrant children who are living in overcrowded, often inadequate federal facilities.

Senate Majority Leader Mitch McConnell, R-Ky., blasted the House bill on Wednesday.

"It's a go-nowhere proposal filled with poison-pill riders which the president has indicated he would veto," McConnell said. The Senate rejected the House bill by a 55-37 vote.

Asked if he's open to adding some language sought by the House, McConnell said, "We're working on finishing up this week and getting it to the president."

Pelosi faces resistance to passing the Senate bill and may be short of votes. She quelled a mini-revolt by progressives and Hispanic lawmakers who won relatively modest changes to the House legislation.

Both House and Senate measures contain more than $1 billion to shelter and feed migrants detained by the border patrol and almost $3 billion to care for unaccompanied migrant children who are turned over the Department of Health and Human Services. The Senate measure is not as strict in setting conditions on the delivery of funding to care for unaccompanied children and contains funding opposed by House Democrats for the Pentagon and to ease a payroll pinch at Immigration and Customs Enforcement.

Both House and Senate bills ensure funding could not be shifted to Trump's border wall and would block information on sponsors of immigrant children from being used to deport them. Trump would be denied additional funding for Immigration and Customs Enforcement detention beds.

The White House has threatened to veto the House bill, saying it would hamstring the administration's border security efforts, and is only reluctantly backing the Senate measure — it received only a single "nay" vote during a committee vote last week.

Lawmakers' sense of urgency to provide humanitarian aid was amplified by recent reports of conditions in a windowless Border Patrol station in Clint, Texas, where more than 300 infants and children were being housed. Many were kept there for weeks and were caring for each other in conditions that included inadequate food, water and sanitation.

The Border Patrol reported apprehending nearly 133,000 people last month — including many Central American families — as monthly totals have begun topping 100,000 for the first time since 2007. Federal agencies involved in immigration have reported being overwhelmed, depleting their budgets and housing large numbers of detainees in structures meant for handfuls of people.

AP Congressional Correspondent Lisa Mascaro contributed to this report.