American troops pulled out of their main military base in Afghanistan on Friday, leaving behind a piece of the World Trade Center they buried 20 years ago, Reuters reported.

The quiet departure from Bagram Air Base brought an effective end to the longest war in U.S. history. It came as the Taliban insurgency ramps up its offensive throughout the country after peace talks sputtered.

The Pentagon said the turnover of Bagram to Afghan security forces was a "key milestone" in the withdrawal, but insisted the U.S. military still has the authority to protect Afghan forces.

U.S. President Joe Biden said the troops' departure is on track, but some American forces will still be in Afghanistan in September as part of a "rational drawdown with allies."

"We consider this withdrawal a positive step. Afghans can get closer to stability and peace with the full withdrawal of foreign forces," Taliban spokesman Zabihullah Mujahid said.