Officials in northern Afghanistan says a suicide bomber has attacked a mosque, killing at least 20 worshippers.

Authorities say the bomber struck Friday, the first day of the four-day Eid al-Adha holiday.

The French news agency reports more than 50 people were wounded in the explosion.

Meanwhile, the U.S. military says it is investigating the deaths of two American service members after a man wearing an Afghan National Police uniform used his weapon against them.

Military officials said Thursday's incident occurred in Uruzgan province. It is not clear if the attacker was a member of the Afghan National Security Forces.

The incident bears the hallmark of a so-called “insider attack,” in which Afghan security forces or insurgents disguised in Afghan or coalition uniforms open fire on NATO personnel. Such attacks have escalated this year, killing more than 50 coalition troops.