Esper's visit -- his first to Afghanistan since being confirmed as Pentagon chief in July -- comes amid deep uncertainty about the fate of the US military mission in Afghanistan after talks between Washington and the Taliban collapsed.

"I'm looking ... to get a really good feel for what's happening on the ground in Afghanistan, and to talk what the way ahead may look like as well," Esper told reporters accompanying him, according to a Pentagon transcript.

The United States and the Taliban were last month on the brink of signing a deal that would have seen US forces begin to withdraw from Afghanistan in return for various insurgent security commitments.

But negotiations collapsed at the last minute when President Donald Trump declared talks "dead" following a Taliban attack that killed a US soldier.

Zalmay Khalilzad, the US special envoy leading negotiations, has since spoken informally with Taliban officials in Pakistan, raising the possibility that Washington is seeking to resume talks.

"We think a political agreement is always the best way forward with regard to next steps in Afghanistan," Esper said.

Currently the United States has around 14,000 troops in Afghanistan.

Esper said that footprint could shrink to about 8,600 forces with no impact on counter-terrorist operations against groups such as the Afghan affiliate of the Islamic State group.