A suicide bomber struck a mosque in northern Afghanistan Friday, killing at least 40 people in one of the deadliest such attacks in recent months.

Authorities say the bomber struck the mosque in Maymana, the capital of Faryab province, at the start of the three-day Muslim festival of Eid al-Adha.

Local officials say the young bomber was targeting a regional police official who was inside the mosque for Eid prayers. The official reportedly survived the blast, but more than 20 of the dead were security personnel. Officials say several civilians, including five children, were also killed.

There was no immediate claim of responsibility for the attack, but officials blamed the Taliban. Faryab's deputy governor, Abdul Sattar Bariz, told reporters that Friday's attack may have been revenge for the killing of the Taliban's “shadow governor” for the province during a clash with security forces earlier this week.

Afghan President Hamid Karzai strongly condemned the attack, saying those behind the bombing were “enemies of Islam and humanity.” In an earlier statement for the Eid holiday, Mr. Karzai had urged the Taliban to lay down their weapons.

The commander of U.S. and NATO forces in Afghanistan, General John Allen, condemned the “heinous act,” which he said is an affront to human life, to religious devotion and to the peaceful aspirations of the Afghan people.

The U.S. Embassy in Kabul also condemned the attack.

Also Friday, the Taliban claimed responsibility for the latest so-called “insider attack” on international forces.

The U.S. military said two American service members were killed Thursday after a man wearing an Afghan National Police uniform turned his weapon on them in the southern province of Uruzgan.

So far this year, at least 53 coalition troops have been killed by members of the Afghan security forces or militants wearing a police or army uniform.