PESHWAR, Pakistan - Pakistani militants, who have escalated attacks in recent weeks, killed at least 41 people in two separate incidents, officials said on Sunday, challenging assertions that military offensives have broken the back of hardline Islamist groups.

The United States has long pressured nuclear-armed ally Pakistan to crack down harder on both homegrown militants groups such as the Taliban and others which are based on its soil and attack Western forces in Afghanistan.

In the north, 21 men working for a government-backed paramilitary force were executed overnight after they were kidnapped last week, a provincial official said.

Twenty Shi'ite pilgrims died and 24 were wounded, meanwhile, when a car bomb targeted their bus convoy as it headed toward the Iranian border in the southwest, a doctor said.

New York-based Human Rights Watch has noted more than 320 Shias killed this year in Pakistan and said attacks were on the rise. It said the government's failure to catch or prosecute attackers suggested it was "indifferent" to the killings.

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