Militants in north-west Pakistan have beheaded six security officials and killed seven civilians in apparent reprisals for an army attack.
Reinforcements were sent to Swat on Wednesday
The army attack on the stronghold of pro-Taleban militant Maulana Fazlullah on Thursday left at least 17 soldiers and a number of civilians dead.
The bodies of the guards reportedly had notes saying they were American agents.
Swat is one of a number of areas near the Afghan border where militants have been gaining control in recent months.
Reports say the civilians who were killed were dragged out of a minibus.
A local resident told Associated Press news agency the bodies of the security officials had notes on them reading: "It is the fate of an American agent. Whoever works for America will face the same fate."
Sirajuddin, a spokesman for Maulana Fazlullah, said the killings were carried out by "common people, who support us because we only want enforcement of Islamic laws".
Security forces dropped leaflets on Saturday urging residents to "eliminate extremism and terrorism from the Swat valley".
Eyewitnesses said Thursday's violence started when troops were airlifted to positions on the hilltops surrounding Maulana Fazlullah's stronghold.
The cleric said earlier this week that he was leaving the area.
On Wednesday the army deployed 2,500 more troops to the region to combat the rising militancy.
Maulana Fazlullah has reportedly used radio broadcasts to call for jihad, or holy war, against the Pakistani authorities.
In July at least 10 Pakistani soldiers were killed in a militant attack in Swat.
It was part of a wave of attacks on the army in response to the security forces' storming of the radical Red Mosque in the capital, Islamabad, that left more than 100 people dead.