EXCLUSIVE: House Republicans on the Border Security Caucus are requesting a briefing by Homeland Security Secretary Alejandro Mayorkas about the escalating crisis at the southern border, and warning that Biden administration policies are fueling it -- days after Mayorkas denied that there was a crisis at all.

Reps. Andy Biggs and Brian Babin, who are the heads of the Congressional Border Security Caucus, wrote to Mayorkas requesting a briefing on the administration’s plans to address what they see as a crisis.

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"Since January 20, 2021, the Biden administration has issued multiple Executive Orders and DHS has announced numerous policy changes that have rolled back policies, such as the Migrant Protection Protocols [MPP], that were implemented by the previous administration," they wrote in a letter, obtained exclusively by Fox News.

The rollback of MPP, which kept migrants in Mexico, as well as other policies such as narrowing enforcement priorities for Immigration and Customs Enforcement (ICE) and ending asylum cooperative agreements with Northern Triangle countries, have been blamed for a surge in migrants at the border.

"These changes announced to the world that the Biden administration is not serious about border security and have led to an increase in aliens, particularly unaccompanied alien children (UAC), crossing the border," the lawmakers wrote.

The administration has been quickly building and opening migrant facilities both to keep unaccompanied children and processing centers for families, amid a surge in arrivals in recent weeks. Meanwhile, Customs and Border Protection (CBP) have been releasing migrants into the interior -- a practice ended by the Trump administration.

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But Mayorkas on Monday denied there was a crisis at all, instead describing it as a "challenge for the government, non-governmental organizations and border communities.

He said instead that the Department of Homeland Security is working to "replace the cruelty" of the Trump administration with "an orderly humane and safe immigration process."

He noted that one of the strictest measures implemented by the Trump administration -- Title 42 public health restrictions that allow migrants to be quickly returned -- are still in place, as he told migrants to hold off coming to the U.S.

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"We are not saying don’t come. We are saying don’t come now, because we will be able to deliver a safe and orderly process for them as quickly as possible," he said.

But the Republicans are not convinced, telling Mayorkas that "your actions send a different message." They note that while Title 42 is in place, they have no far not applied such restrictions to unaccompanied children.

"This decision has led to a significant influx of UAC that are now filling facilities and stretching government resources," they wrote.

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They also noted the renewed ICE priorities, which tell agents they will need approval from a manager if they wish to arrest and deport an immigrant who does not fit into three categories. The administration had sought to impose a 100-day moratorium on deportations but had been blocked after a lawsuit from Texas.

The lawmakers request a meeting in-person with Mayorkas "as soon as possible to discuss the growing crisis at the southern border."

Fox News' Brooke Singman contributed to this report.