A bipartisan group of senators is working through the weekend to forge a deal on asylum policy changes designed to reduce migrant crossings along the southern border, hoping to make a rare breakthrough on one of Congress' most intractable issues, three congressional officials told CBS News.

Sens. Michael Bennet of Colorado, James Lankford of Oklahoma, Chris Murphy of Connecticut, Kyrsten Sinema of Arizona and Thom Tillis of North Carolina are negotiating a compromise to overhaul how migrants are processed along the U.S.-Mexico border, where illegal crossings have soared to all-time highs over the past two years. The compromise they're envisioning would be part of a broader national security funding package requested by President Biden that includes aid to Israel, Ukraine and border security money, which Senate Republicans have conditioned on significant restrictions on asylum.

Bennet and Murphy are Democrats, and Lankford and Tillis are Republicans. Sinema is a former Democrat who became an independent late last year.

The bipartisan group spoke on Wednesday night to hash out a framework for the potential deal, and will continue their talks through the weekend alongside their staff, the congressional officials said. If a breakthrough materializes in the Senate, it's unclear if the Republican-led House would take up and pass a bipartisan border proposal that is not as strict as a measure it passed earlier this year.

In an interview with CBS News, Sinema said the Senate negotiators believe there's an urgent need to address what she called a "porous border" and "loopholes" in U.S. immigration law being exploited by those smuggling migrants into the country.

"There's growing concern, from folks on both sides of the aisle, that we have to act now, as a national security measure, to protect our border and ensure the safe passage of migrants into our country for those who do qualify for asylum," Sinema said.

In fiscal year 2023, Border Patrol processed more than two million migrants who crossed into the U.S. unlawfully, only the second time that threshold has been surpassed in the agency's history, federal statistics show. The unprecedented migration flows have strained federal and local resources, in border and interior cities alike, and created a political headache for Mr. Biden as he seeks a second term. 

Partisan gridlock has doomed numerous other attempts to pass a bipartisan reform of the U.S. immigration system, which has not been updated in any significant way since 1996. The ongoing talks in the Senate could meet the same fate, but several factors have opened a rare, though limited, window for lawmakers to reach a compromise on some immigration issues.

The Biden administration, congressional Democrats and many Republicans want Congress to approve more military assistance to Ukraine to help its war effort against Russia. However, Republican leadership in the Senate has linked passing additional aid to Ukraine, which some Republicans oppose, to changes to U.S. border policy. The Biden administration has also implored Congress to allocate billions of dollars in funding to hire additional immigration officers and judges and bolster border security, but Republicans have rejected approving those funds without a policy shift.

Moreover, the White House is under growing political pressure to reduce the flow of migrants into the U.S., including from Democratic mayors and governors in cities like New York and states like Illinois that are struggling to shelter the new arrivals. Internally, some administration officials also believe the spike in border crossings won't drop to manageable levels unless the asylum system is reformed.

Earlier this week, a Republican Senate working group led by Lankford released its border policy demands, asking for drastic limits on asylum eligibility, long-term detention centers to hold migrant families with children and the reinstatement of Trump-era policies like the so-called "Remain in Mexico" program.

While Democrats are unlikely to support family detention and the more sweeping restrictions on asylum, they could be open to some limits and faster deportations. During a Senate hearing this week, Murphy, the Connecticut Democrat, said a discussion about "adjustments to the asylum standard" was a "legitimate conversation," though he noted it would need to be accompanied by a surge in resources.

Sinema said that while the ultimate eligibility criteria for asylum — centered on showing well-founded fear of being persecuted — does not need to change, the steps before migrants see a judge do need to be altered. 

"Right now, that system is broken," she told CBS News. "And the cartels are exploiting the loopholes in the system. And it's created a situation that is inefficient, inhumane, and it's dangerous for both our communities and for migrants." 

The purpose of the talks, Sinema added, is to find a "middle ground.The White House, which congressional and administration officials have said is not involved in the Senate talks, said earlier this week it disagreed with "many" of the GOP working group's proposals, but left the door open to having a "serious conversation about reforms that will improve our immigration system" with Republicans.

In their list of demands, Republican senators also included dramatic restrictions on the use of humanitarian parole, a law the Biden administration has invoked to welcome hundreds of thousands of migrants and refugees from Afghanistan, Latin America and Ukraine. 

Any border security deal by the bipartisan Senate group would almost certainly face criticism from the left and right.

Immigration hardliners, who have advocated for mass deportations and the gutting of U.S. asylum law, would likely view it as insufficiently restrictive. Even if the Senate strikes a deal, it's unclear if the Republican-led House and Speaker Mike Johnson would support a bill backed by Democrats.

On the other hand, restrictions on asylum and efforts to speed up deportations would likely garner criticism from progressives and immigrant rights advocates, most of whom do not support changes to asylum law. A deal that does not include the legalization of undocumented immigrants, such as so-called "Dreamers," would also create rifts among Democrats and their allies, who have pushed for a path to citizenship for decades.

"Essentially the Republicans are saying, 'We will get everything we want and you don't get anything,' and that's not really a negotiation position," said Aaron Reichlin-Melnick, policy director at the American Immigration Council, which advocates for progressive migration policies.

Reichlin-Melnick said advocates would not back any of the Republicans' proposals, which he said would amount to the "mass detention of families and children in prison camps" and "the elimination of asylum."

But Theresa Cardinal Brown, an immigration expert at the Bipartisan Policy Center, said the record levels of migrant apprehensions along the southern border over the past years have shown that the current asylum process is "unworkable" and needs to be reformed.

"It has overwhelmed our ability to process people," said Cardinal Brown, a former federal immigration official under Presidents Barack Obama and George W. Bush. "As a practical matter, we're not processing people for asylum. We're adding them to an interminable queue."