A military official said the incident happened near Afghan border in Ghulam Khan area.
"Six soldiers were killed and three are injured due to improvised explosive device (IED) explosion between Afghan border and Ghulam Khan in North Waziristan," he said.
Pakistan yesterday launched a major ground and air operation against local and foreign militants hiding in the tribal region.
According to military spokesman so far at least 177 militants, mostly Uzbeks, have been killed, including the 27 killed today in an air strike.
The long-overdue operation was a constant source of friction between the US and Pakistan.
The US has been pressing Pakistan to flush out the militants in the region, which they use to launch attacks on NATO forces in Afghanistan.