United States Defence Secretary Robert Gates met with the US ambassador to Afghanistan on Tuesday before planned meetings with NATO and US military leaders and Afghan President Hamid Karzai to discuss the resurgent Taliban insurgency.
It was Gates' first trip to Afghanistan since he took over for Donald H Rumsfeld last month.
Gates has said several times recently that he is worried that US gains in stabilising Afghanistan could be in jeopardy as the radical Taliban movement makes a comeback in some parts of the country, particularly the south.
At NATO headquarters in Belgium on Monday, Gates said one subject he and military leaders discussed "was the increased level of violence last year and some indication that the Taliban want to increase the level of violence in 2007," he told reporters.
The top US general in Afghanistan, Gen Karl Eikenberry, said last month that he wouldn't be surprised to see the same level of violence in 2007 that Afghanistan saw in 2006.
Taliban rebels launched a record number of attacks last year, and some 4,000 people died in insurgency related violence, according to numbers compiled by the agency based on information from NATO, the US and the Afghan government.
Gen Mohammad Zahir Azimi, the Afghan Defense Ministry spokesman, called Gates' trip "an important visit" because the United States was helping Afghanistan train and equip its army.
Gates said on Monday that new US military moves in the Persian Gulf were prompted in part by signals from Iran that it sees the United States as vulnerable in Iraq.
The Pentagon decided last week to send a second aircraft carrier battle group and a Patriot anti-missile battalion to the Gulf.
Iran, which also borders Afghanistan, has great economic influence in the western Afghan city of Herat, where it has built roads, provides electricity, and fills the region with cheap goods.
Gates said that as recently as 2004 the Iranians were "actually doing some things to be helpful" in Iraq, at a time when they felt concern at the presence of US troops on their western and eastern borders, in Iraq and Afghanistan.
At that point he felt diplomatic dialogue would be useful. He said "none of those conditions" apply now.