By Andrew Gray

WASHINGTON, June 24 (Reuters) - Insurgent attacks in eastern Afghanistan rose by 40 percent in the first five months of this year over the same period a year ago, the U.S. commander of NATO forces in the region said on Tuesday.

While insisting NATO was making progress in establishing stability, Army Maj. Gen. Jeffrey Schloesser said he was "nowhere near" being able to state those efforts had achieved irreversible momentum.

Speaking to reporters at the Pentagon by videolink from Afghanistan, Schloesser also said attacks by Taliban and other insurgents were becoming increasingly complex and targeted sites such as schools to disrupt economic development.

Schloesser's comments came against a backdrop of increasing concern in Washington and other Western capitals about the war in Afghanistan and instability in border areas of Pakistan, where U.S. officials say Taliban fighters enjoy safe haven.

Schloesser said success in Afghanistan would ultimately come not through military operations but when Afghans "sitting on the fence" concluded their government offered a better quality of life and decided to oppose insurgent groups.

"I can't predict how long it's going to take. I can say that I believe we're making progress," he said.

Schloesser said the rise in violence was not unexpected as attacks had increased every year since 2002, the year after U.S.-led forces ousted the Taliban from power following the Sept. 11, 2001, attacks on the United States.

Eastern and southern Afghanistan have been the scenes of the heaviest insurgent violence. But U.S. officials had touted the east as a success story last year, saying the area had become much more stable.

Schloesser said one reason for the rise in attacks this year was that international and Afghan forces had gone into areas where they had not operated before to hunt insurgents.

"We are actually hunting down the enemy of the Afghan people and trying to rout them," he said. "We're giving them four options -- they can flee, get out of their country, they can reconcile or they can be captured or killed."

He did not provide the raw numbers behind the percentage increase he cited.

Schloesser commands the U.S-led eastern sector of Afghanistan for NATO's 53,000-strong International Security Assistance Force. He is also in charge of a separate U.S. counter-terrorism mission.

He said success in Afghanistan would require much work from the international community and patience from Americans.

"We're clearly not done and I am nowhere near yet able to say that we have reached irreversible momentum," he said.

(Editing by David Wiessler)

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