Just days from retirement, U.S. Defense Secretary Robert Gates was bidding a final farewell on Monday to front-line U.S. troops in Afghanistan.

He flew from the Afghan capital, Kabul, to a troop base in one of the more remote and dangerous parts of the country, in Paktika province, which borders Pakistan.

On Sunday, he visited two troop bases in southern Afghanistan to say goodbye and thank soldiers and Marines for their service in the fight against the Taliban.

Gates, 67, is retiring June 30, ending a 4 1/2 year tenure as Pentagon chief. One of his last major issues will be to recommend to President Barack Obama how to begin and carry out a U.S. troop withdrawal starting in July.

In a session with soldiers of the 506th Infantry Regiment, 4th Brigade, 101st Airborne Division, Gates said that despite eliminating Osama bin Laden, it was still too soon to wind down the Afghan war. He said more military pressure must be applied to the Taliban before they are likely to feel it necessary to talk peace.

"We've got to keep the pressure on them," he told an assembly of several hundred troops at Sharana. "We're not quite there yet."

"It's too early to tell" how bin Laden's death will affect the course of the war in Afghanistan, where the al-Qaida leader once enjoyed a haven from which to operate under the ruling Taliban regime, he said.