Major-General Waheed Arshad, the chief military spokesman, said on Sunday: "A suicide bomber in a white car struck a military convoy near Mingora."
The military said four security forces personnel and three civilians were killed. It said 15 soldiers and 14 civilians were wounded.
More than 750 people have been killed in attacks this year - and more than half of those since July, when the army raided a mosque in the capital, Islamabad, killing 100 people.
The military launched a major offensive in the Swat valley, in the north of the country, in November, looking to drive out followers of Maulana Fazlullah. He has since gone underground.
There have been more than 40 suicide attacks in Pakistan this year, many of them targeting the military and security forces.
On Friday, when a bomber wearing a vest packed with ball-bearings blew himself up in a mosque, killing 56 people but missing the intended target Aftab Sherpao, the former interior minister.
Sherpao, a close ally of Pervez Musharraf, the president, and a candidate in next month's parliamentary election, oversaw a government crackdown on armed groups this year when he was in the cabinet.
He survived another suicide attack in April that killed at least 24 people. The latest bombing came just two weeks ahead of the January 8 vote.