Exclusive: A group of Republican senators signed onto a letter to Homeland Security Alejandro Mayorkas demanding more details on the two Jordanian nationals who were arrested after attempting to breach Marine Corps Base Quantico in Virginia.

"This incident and a number of similar incidents in recent months are in stark contrast with your statements to Congress that the border is ‘secure,’’ ‘no less secure than it was previously,’ ‘closed,’ and that DHS has ‘operational control’ of the border," the letter, which was penned by Sen. Ted Budd, R-N.C., said. "The military community at Marine Corps Base Quantico and the American people deserve answers regarding the terrorism and counter-intelligence threats posed by the Biden administration’s open border policies."

The letter comes as mystery still surrounds the two Jordanian nationals who attempted to breach Quantico by posing as Amazon drivers earlier this month, with the U.S. Immigration and Customs Enforcement agency (ICE) still declining to release the pair’s identity to the public.

JORDANIAN WHO TRIED TO BREACH MARINE CORPS BASE QUANTICO WAS IN US ILLEGALLY, SOURCES SAY

Alejandro Mayorkas in front of US flags

U.S. Department of Homeland Security Secretary Alejandro Mayorkas. (John Moore/Getty Images)

One of the two suspects crossed into the U.S. illegally in April, multiple Department of Homeland Security sources told Fox News Thursday, crossing the border and the San Diego sector and later released with a notice to appear in court because of a lack of derogatory information found on him.

The other Jordanian national was also in the country illegally, the sources told Fox News, having overstayed a student visa.

Neither man had a criminal history in the U.S., the sources said, while both suspects are now in ICE custody awaiting removal proceedings.

US Marine Corps Base gate

The main gate of the U.S. Marine Corps Base in Quantico, Virginia. (JIM WATSON/AFP via Getty Images)

BIDEN BORDER CHIEF MAYORKAS IN HOT SEAT OVER JORDANIAN NATIONALS WHO TRIED TO BREACH QUANTICO

But the letter, which was signed by over a dozen GOP senators, notes that many questions remain unanswered, including whether or not one of the individuals was on a terrorist watch list. 

The senators also noted that similar incidents have taken place in recent months, including a March attempt by a Chinese national who was in the country illegally to break into Marine Corps Air Ground Combat Center Twentynine Palms in California. 

The letter comes at the same time as a similar effort from House Republicans, with Homeland Security Committee Chairman Mark E. Green, R-Tenn., and other committee leaders issuing a letter to Mayorkas and Defense Secretary Lloyd Austin demanding answers.

"The Committee fears that the Department of Homeland Security’s relaxed vetting standards, which complement President Biden’s avowed desire to 'surge the border' with inadmissible migrants, have created an environment ripe for exploitation by individuals aiming to undermine the United States at its most critical points," reads the House letter.

Meanwhile, the Senate letter pointed out that such attempts by Chinese nationals to gain access to U.S. military installations has happened as many as 100 times, including an instance of a group of Chinese nationals attempting to push their way past guards at Fort Wainwright, Alaska, claiming they had hotel reservations on the base.

Migrants in El Paso, Texas

A group of over 100 migrants attempting to enter the US illegally rushing a border wall Thursday, March 21, 2024. In the process, the migrants knocked down Texas National Guardsmen before they were halted by the border wall. (James Breeden for New York Post / Mega)

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"All of these events occur in the context of increasing U.S. Border Patrol encounters of aliens on the terrorist watchlist as well as a record number of Chinese national encounters at the southern border during the Biden administration," the letter reads.

Sens. Kevin Cramer, R-N.D.; Rick Scott, R-Fla.; Josh Hawley, R-Mo.; J.D. Vance, R-Ohio; Roger Wicker, R-Miss.; Mike Braun, R-Ind.; Marco Rubio, R-Fla.; Mike Lee, R-Utah; Roger Marshall, R-Kan.; Ted Cruz, R-Texas, John Hoeven, R-N.D.; and John Kennedy, R-La.

DHS did not immediately respond to a Fox News Digital request for comment.