US Defense Secretary Leon Panetta arrived in the Afghan capital on an unannounced trip Thursday, a day after a suicide bombing attack and an alleged errant Nato air strike.
Before his arrival, Panetta told reporters that he wanted to hear an assessment from commanders about a recent rise in insurgent attacks and plans for troop withdrawals.
Panetta said an insurgent assault on Wednesday "was much more organised than we've seen before", with a suicide bomber on a motorcycle and a suicide bomber on foot striking a vehicle park outside a Nato base.
Panetta, who flew to Kabul from New Delhi, said he wanted "to get a sense of just exactly what are the Taliban doing".
"There's been an increase in the attacks," he said, adding that the overall level of violence in the country was still down compared to previous years.
The Pentagon chief said he would confer with the top commander of Nato-led forces, General John Allen, to hear how he planned to maintain security despite Taliban attempts to undermine a gradual transfer of authority from alliance troops to Afghan government forces.
In a brief visit of several hours, he was also due to meet US ambassador to Kabul, Ryan Crocker, before speaking to American troops and holding talks with his Afghan counterpart, Abdul Rahim Wardak, officials said.