Swat, Pakistan: Militants have executed 13 captives accused of being spies in apparent retaliation for an assault by security forces on the stronghold of a militant cleric in northwestern Pakistan, officials said on Saturday.

The men, including six security personnel and seven civilians, were captured by militants at a roadblock on the outskirts of Swat district, said Home Secretary Badshah Gul Wazir.

Officials said earlier that 11 people had been kidnapped on Friday.

A witness said he had seen six of the bodies with notes attached accusing them of being American agents.

A spokesman for the pro-Taliban cleric, Maulana Fazlullah, claimed the killings were carried out by local residents who back the militants' aims — although there was no other indication that villagers were responsible for the deaths.

"It was done by common people, who support us because we only want enforcement of Islamic laws," said Sirajuddin, who goes by one name.

Wazir said the civilians were accused of being spies.

Militants seized the men after an attack Friday on Fazlullah's stronghold of Imam Dheri village in which security forces backed by helicopters and militants traded fire using rocket-propelled grenades, mortars and other weapons.