ISTANBUL — NATO's European allies came under pressure Friday to make a fresh but possibly decisive effort to send military and police trainers to Afghanistan to seize the initiative from Taliban insurgents.

At talks between alliance defence ministers in Istanbul, Turkey, the United States and NATO Secretary General Anders Fogh Rasmussen urged nations to find some four thousand trainers seen as a vital cog in NATO's strategy.

The NATO-led International Security Assistance Force (ISAF) has amassed around 40,000 extra troops and has begun deploying them in Afghanistan as part of the new counter-insurgency approach aimed at ending eight years of fighting.

ISAF's ultimate success in implementing the strategy, which aims to protect civilians rather than hunt down fighters, hinges on its ability to train the national army and police, but experts have been notoriously difficult to find.

Only when the Afghan forces are built to sufficient strength and skill can the more than 110,000 international troops fighting the Taliban and other insurgents, a hard core linked to Al Qaeda, start returning home.

"There is no doubt 2010 will be a challenging year," Rasmussen told the ministers.

"There will be more fighting, militants and terrorists will seek to kill ISAF soldiers and innocent Afghans, but this is also the year we should begin to see Afghanistan's future take shape," he said.

ISAF wants to expand the Afghan army to 134,000 troops in October 2010 and 171,600 by October 2011, while the police numbers would expand from some 80,000 now, to 109,000 in October, and 134,000 the following October.

A senior US official said up to 1,700 instructors were needed for the police and army, while up to 2,500 additional mentors were required to work alongside the national security forces.

The US demand comes as thousands of Afghan and NATO troops prepare a major offensive in southern Afghanistan, the hub of the insurgency, in the biggest assault since President Barack Obama announced the surge in December.

US Defense Secretary Robert Gates was to press partners to move on trainers "as quickly as they can to get their forces into the fight because time is of the essence," Pentagon spokesman Geoff Morrell said.

"We need to seize that window of opportunity... and get the Afghan national security forces to the position they need to be to transition into a leadership role on the security side," he said.

"It is important that our allies contribute their forces to this cause in as timely a manner as possible just as we are," he said.

Slovak Defence Minister Jaroslav Baska said his country would have trainers in place later this year, and he also urged other allies to do more.

"European countries have plenty of possibilities to send these trainers," he told AFP. "We must send these trainers, we have to help to train the police in Afghanistan, otherwise we cannot leave."

NATO's senior commander in Afghanistan, US General Stanley McChrystal, has warned that the next 18 months could prove pivotal to bringing stability, and he was cautiously upbeat Thursday about developments.

"The situation is serious but I think we have made significant progress and set the conditions in 2009 and we'll make new progress in 2010," he said on the sidelines of the NATO meeting.