* Attacks in Pakistan more than doubled to 1,839

* Overall decline reflects diminished violence in Iraq

* Number of people killed in Afghanistan rose slightly (Adds details, quotes, background)

WASHINGTON, April 30 (Reuters) - The U.S. State Department said on Thursday the number of people killed in terrorist attacks in Pakistan last year rose by more than 70 percent despite an overall drop in such violence worldwide.

U.S. officials have grown increasingly worried about the stability of nuclear-armed Pakistan as Taliban militants have advanced beyond their Swat valley stronghold to Buner valley, just 60 miles (100 km) northwest of the capital, Islamabad.

The Pakistani army on Thursday fought through mountain passes for a third day to try to evict the Taliban from Buner, acting after U.S. Secretary of State Hillary Clinton last week accused the government of abdicating to the Taliban. [ID:nSP437584]

Data compiled by the U.S. intelligence community suggested that Pakistan faces a growing threat from terrorist violence.

The number of people killed in such attacks -- including the Sept. 20 bombing of the Marriott Hotel in Islamabad -- rose to 2,293 from 1,340, according to the data released by the State Department.

The number of terrorist attacks in Pakistan more than doubled to 1,839 from 890, U.S. officials told reporters.