U.S. Secretary of State Hillary Rodham Clinton is expected to press other NATO nations to provide more trainers for Afghanistan's police and military forces as part of preparations to withdraw Western troops from there by summer 2011, according to AP. Clinton and representatives of 27 other NATO countries _ all of which contribute to the war effort _ also are expected on Friday to review broader plans for turning the conflict over to Afghan forces starting the middle of next year, a goal set by the White House. NATO's assessment of its exit strategy comes just five months after President Barack Obama sharply escalated troop strength in the rugged mountain nation to challenge a resurgent Taliban movement. NATO has struggled, in some cases, to coordinate military operations with Afghan civilian authorities and agencies. Anders Fogh Rasmussen, NATO's top ranking civilian, said Thursday that an additional 450 trainers are needed for Afghanistan's security forces. Clinton aides, meanwhile, said she planned to appeal to the alliance to provide the required trainers. The aides spoke on condition of anonymity because Clinton's plans were still being made, as NATO foreign ministers gathered here to discuss alliance nuclear policy, missile defense and other issues. In a speech Thursday before the two-day NATO meeting began, Fogh Rasmussen called Afghanistan the most challenging military operation undertaken by NATO in its history. NATO was founded 61 years ago this month with the signing of a treaty of collective defense against a feared land invasion by the Soviet Union. Today, Fogh Rasmussen said, instability in places far from Europe can threaten NATO member states. «We all want to see a stable and secure Afghanistan _ an Afghanistan that is no longer a threat to its region and to the rest of the world,» he said in his speech. «We will stay in Afghanistan as long as it takes to achieve that goal. We want to continue to empower the Afghans. And gradually hand over to them greater responsibility for the security of their own country when conditions permit.» During Thursday's talks, Clinton ruled out an early withdrawal of about 200 short-range U.S. nuclear weapons from bases in five European countries. She said any reductions should be tied to a negotiated nuclear pullback by Russia, which has far more of the weapons in range of European targets. No such talks are in the offing, and Moscow has shown little interest thus far in bargaining away its tactical nuclear arms. Clinton also said the Obama administration wants NATO to accept missile defense as a core mission of the alliance. The U.S. sees anti-missile systems as part of a broader effort to combat the dangers posed by nuclear, biological and chemical weapons and the rockets that can deliver them. Some European members of NATO, including Germany, have said it's time for the U.S. to withdraw its remaining Cold War-era nuclear weapons from Europe and cite Obama's pledge in Prague last year to seek a nuclear-free world. Late last year, Germany was joined by NATO members Belgium, the Netherlands, Norway and Luxembourg in requesting that the nuclear issue be put on the agenda of the Tallinn meeting. But some newer NATO members in central and eastern Europe, which lay within Moscow's orbit during the Cold War, oppose a U.S. nuclear withdrawal. They argue that the presence of the weapons is the surest guarantee of their territorial integrity. Fogh Rasmussen told reporters here that U.S. nuclear weapons play a vital defensive role in Europe and should not be removed as long as other countries possess them. «I do believe that the presence of the American nuclear weapons in Europe is an essential part of a credible deterrent,» Fogh Rasmussen said.