Incursions into Afghanistan troubling: Bush

US President George W Bush said on Tuesday he was "troubled" by the movement of extremists from Pakistan to Afghanistan and would discuss the threat with Prime Minister Gilani here this month.

Speaking at a White House press conference, Bush also said the United States would investigate charges by Afghan President Hamid Karzai that elements of the Pakistani intelligence services had been involved in attacks in Afghanistan.

"We'll investigate his charge and we'll work with his service to get to the bottom of his allegation," the president said. "No question, however, that some extremists are coming out of parts of Pakistan into Afghanistan," Bush said. "And that's troubling to us, it's troubling to Afghanistan, and it should be troubling to Pakistan.

"I certainly hope that the government understands the dangers of extremists moving in their country," the president said. "I think they do." "As a matter of fact, we'll have an opportunity to explore that further" with Prime Minister Yousuf Raza Gilani, Bush said.

"Pakistan is an ally. Pakistan is a friend," he said. "And I repeat, all three countries -- the United States, Pakistan and Afghanistan -- share a common enemy." "We will continue to keep the pressure on al-Qaeda with our Pakistan friends," Bush said.

Bush also said the United States was "surging troops in Afghanistan". "One front right now is going better than the other, and that's Iraq, where we're succeeding," Bush said. "And Afghanistan is a tough fight."

The situation in Afghanistan was reminiscent of Iraq a couple of years ago when "the enemy knows that they can affect the mentality of the American people if they just continue to kill innocent folks", Bush said.

"But it is a two-front war," he said, adding that the United States was also conducting covert operations. Bush offered the following advice to his successor in the White House: "I would hope that whoever follows me understands that we're at war and now is not the time to give up in the struggle against this enemy."And that while there hasn't been an attack on the homeland, that's not to say people don't want to attack us."