KABUL  - There has been a spike in mortar and rocket attacks from militants in Pakistan at US and Afghan border outposts in Afghanistan, the top NATO commander said. But US Gen David D McKiernan said militants shouldn't feel safer just because they're in Pakistan's territory, because US and NATO forces "do return fire." "We have seen an increase in the eastern part of Afghanistan of cross-border indirect fires coming into some of our, not only our but Afghan, stationary sites, outposts, border police sites," said McKiernan, who took command of the 40-nation International Security Assistance Force mission last month. The four-star general did not have figures, but said in an interview this week "there definitely has been an increase since I've been here in the last 30 days." McKiernan believes the number of attacks has risen because militant groups have been free to operate in Pakistan's lawless tribal areas and cross the Afghan-Pakistan border unimpeded to resupply and recruit. As allied forces move into new territories, they are encountering resistance from fighters who are attacking more vulnerable targets with complex ambushes and suicide bombings, he said. "There is a continuing issue of the very porous border with Pakistan and it has allowed insurgent militant groups a greater freedom of movement across that border, a greater freedom to resupply, to provide leadership, to provide manning across that border," McKiernan said.