The clashes in the North Waziristan tribal region came as President Pervez Musharraf said Pakistan was in "direct confrontation" with extremists who have launched a wave of attacks since a government raid on an Islamabad mosque.
In the first attack, insurgents fired rockets at a military convoy and then opened fire with automatic weapons near the village of Lwara Mundi, chief military spokesman Major General Waheed Arshad said. "Seventeen soldiers were martyred and more than a dozen miscreants were also killed when troops returned fire," Arshad told AFP.
"Initial reports say that the fighting was heavy," a senior security official based in the area said. The mountainous area where the ambush took place is near where Pakistani forces earlier this year erected the first 35-kilometre (20-mile) stretch of a controversial anti-Taliban fence along the border with Afghanistan.
About six hours later another clash erupted after militants attacked troops in Mir Ali, about 50 kilometres away in the same region. Five rebels were killed and there were no military casualties, Arshad said. In other violence overnight a roadside bomb blast in North Waziristan injured six civilians and a soldier.
Separately a landmine exploded overnight outside the home of politician Mohammad Ajmal Khan, who served as federal sports minister in the 1990s, in Miranshah, the main town in the tribal area.
The blast destroyed his front gate but caused no casualties, officials said. Pro-Taliban militants in North Waziristan on Sunday tore up a controversial 10-month-old peace deal with the government, further fuelling tensions after last week's assault on the radical Red Mosque in Islamabad.