"The helicopter was shot down by an anti-aircraft missile, killing pilots and many foreign ambassadors," an Urdu-language statement emailed by their main spokesman Muhammad Khorasani said, AFP reports.
It was not immediately possible to verify the claim, but the Gilgit-Baltistan region in Pakistan's north where the chopper came down is not known as a stronghold for the militant organization.
An earlier statement by Sharif's office had said his plane was en route to the Gilgit area at the time of the attack but turned back to Islamabad after news of the crash broke.
The ambassadors to Pakistan from the Philippines and Norway and the wives of the ambassadors from Malaysia and Indonesia were killed Friday when a Pakistani army helicopter carrying foreign dignitaries made a crash landing in the country's north, the military said.
Video of the scene showed a school building gutted by fire and a rescue helicopter leaving the area.
Norway's government confirmed the death of its ambassador Leif Holger Larsen. Norwegian Foreign Minister said Larsen was "one of our best and most experienced diplomats."
Known for its spectacular mountain ranges and unique culture, Gilgit-Baltistan is a strategically important autonomous region that borders China, Afghanistan and Indian-held Kashmir.
A senior local administration official said the crash set the school building on fire, but that no children were in class at the time.
“The school, built by Pakistan Air Force for the children of the area, was closed as part of a security plan for the prime minister’s visit,” he said. Earlier, an official had said that the school was open.