Speaker of the House Nancy Pelosi urged lawmakers Tuesday not to "unnecessarily divert needed resources" away from evacuees fleeing Afghanistan after two lawmakers departed in secret for Kabul.

Reps. Seth Moulton, D-Mass., and Peter Meijer, R-Mich., left for Afghanistan to conduct "oversight on the executive branch" as the Biden administration works to evacuate thousands in the wake of the Taliban takeover. 

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"As veterans we care deeply about the situation on the ground at Hamid Karzai International Airport," the two lawmakers said in a joint statement obtained by Fox News. "America has a moral obligation to our citizens and loyal allies, and we must make sure that obligation is being kept."

U.S. Rep. Peter Meijer, R-Mich. (Associated Press)

U.S. Rep. Peter Meijer, R-Mich. (Associated Press)

Pelosi sent a letter to lawmakers Tuesday warning them away from following in their colleagues' footsteps and traveling to the "region during this time of danger."

"Ensuring the safe and timely evacuation of individuals at risk requires the full focus and attention of the U.S. military and diplomatic teams on the ground in Afghanistan," the speaker said in a letter obtained by Fox News. 

Pelosi said she understood lawmakers' concerns for both Americans and Afghans still stuck in the now Taliban-run nation, and reminded them that the Pentagon and the State Department have advised against member travel. 

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"We conducted this visit in secret, speaking about it only after our departure, to minimize the risk and disruption to the people on the ground, and because we were there to gather information, not to grandstand," Moulton and Meijer, who both served in the War in Iraq, said. 

A spokesperson for Moulton told Fox News the lawmakers paid for their flights to the United Arab Emirates where they then boarded a military flight with available seating for the remainder of their trip.

U.S. Rep. Seth Moulton, D-Mass. (Associated Press)

U.S. Rep. Seth Moulton, D-Mass. (Associated Press)

The pair stayed in Kabul from approximately 4 a.m. to 8 p.m. EDT. 

"We left on a plane with empty seats, seated in crew-only seats to ensure that nobody who needed a seat would lose one because of our presence."

President Biden announced that the U.S. had evacuated 70,700 people from Afghanistan since Aug. 14 – 12,000 of whom had been evacuated in the last 12 hours. 

The administration has yet to confirm how many more evacuees are attempting to flee the country, though Biden said he believes the U.S. can get it done by the Aug. 31 deadline. 

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The president said he has directed the State Department and Pentagon to come up with contingency plans should the U.S. need to maintain a military presence past the deadline. 

Moulton and Meijer, however, described the situation as bleak and suggested that the U.S. would not be able to evacuate all Americans and at-risk Afghans even with a Sept. 11. extension.

"Washington should be ashamed of the position we put our service members in, but they represent the best in America," the pair said. "These men and women have been run ragged and are still running strong. Their empathy and dedication to duty are truly inspiring."

Fox News' Kelly Phares and  Chad Pergram contributed to this report.