Secretary of State Hillary Rodham Clinton on Thursday warned NATO allies not to abandon Afghanistan and predicted a violent spring in the war as the Taliban attempts to regain ground lost to NATO forces over the past year.

“We have to steel ourselves and our publics for the possibility that the Taliban will resort to the most destructive and sensational attacks we have seen,” she said at a NATO summit in Berlin.

U.S. military officials have regularly predicted that the levels of violence this year would surpass last year’s. They argue that this is partly because they have record numbers of NATO troops in Afghanistan and because they are pushing into former Taliban strongholds.

On Thursday there were at least three separate insurgent attacks — including suicide bombers in eastern Paktika province who blew up at a training area for Afghan Local Police, the government-backed militia defense program being replicated in many villages.

Clinton also said there are reasons for optimism in Afghanistan.

“After so much effort and so much sacrifice, I believe we are seeing real progress in Afghanistan. That progress comes with important opportunities, but it remains fragile and reversible. If we want it to last — and grow — we need to see this mission through together.”