In a statement marking the Muslim festival of Eid, the group appealed to Islamists there to unite against the "enemy" - the US-led alliance. IS has taken over large parts of Syria and Iraq, but has also been battling al-Qaeda-linked rival militant groups.
The statement was issued by the leader of Tehreek-e-Taliban Pakistan (TTP), Maulana Fazlullah.
Addressing IS in Syria and Iraq, he said, "We are proud of your conquests against the enemies. We are with you in good and bad times." "In these troubled days, we call on you to be patient and stay united as your enemies are now united against you. Forget rivalries," the statement added.
The statement said the global Muslim community would "stand by you in these tough times and help with what we can".
More than 160,000 Syrians, mainly Kurds, have fled across the border since IS launched its offensive on Kobane last month.
The Pakistani Taliban has been waging its own insurgency against the Islamabad government since 1997.
More than 190,000 people have been killed in more than three years of conflict in Syria.