Sen. John McCain and a bipartisan group of senators visited U.S. troops in Afghanistan Tuesday for the Fourth of July.

The senators traveled to Bagram Airfield, where military units are involved in the NATO-led Resolute Support mission to assist Afghan forces. They made the Bagram stop after traveling to South Waziristan to tout successes of the Pakistan army.

McCain was accompanied on the unannounced trip by Sens. Lindsey Graham, R-S.C., Elizabeth Warren, D-Mass., David Perdue, R-Ga., and Sheldon Whitehouse, D-R.I.

"Wonderful seeing so many outstanding American service members serving in Afghanistan — we can't thank them enough for their sacrifice," McCain tweeted.

The senators presided over a promotion and re-enlistment ceremony at the base, according to McCain's tweets.

The visit comes as President Trump and Defense Secretary Jim Mattis weigh sending thousands more troops to Afghanistan. McCain has strongly criticized the administration for not putting forth a strategy to win the fight against the Taliban and secure peace in the country after 16 years of war.