US Defence Secretary Mark Esper arrived in Kabul on Sunday for an unannounced visit to meet US troops and Afghan President Ashraf Ghani. Mr Esper's visit, his first to Afghanistan since becoming 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 about what the way ahead may look like as well," Mr Esper said. The US and Taliban were last month on the brink of signing a deal that would have led to US forces withdrawing from Afghanistan in return for security commitments. But negotiations collapsed at the last minute when President Donald Trump declared talks "dead" after a US soldier was killed in a Taliban attack. Zalmay Khalilzad, the US special envoy leading negotiations, has since spoken informally with Taliban officials in Pakistan, raising the possibility that Washington will resume talks. "We think a political agreement is always the best way forward with regard to next steps in Afghanistan," Mr Esper said. The US has about 14,000 troops in Afghanistan. He said that could shrink to about 8,600 troops without harming operations against groups such as the Afghan affiliate of ISIS.