Chances of a U.S.-Iran conflict escalating into something bigger are “very, very high” — though a full-blown war is unlikely, said a former advisor to the Iranian government.

Washington and Tehran nearly came to blows last week after Iran claimed it downed an American drone that entered its territory. The U.S. said its aircraft was operating in international airspace.

“We have to remember Iran is a regional superpower. U.S. says ‘I’ll put you in a box, please die.’ They (Iran) are not going to stay in a box and just die,” said Fereidun Fesharaki, who was a former energy advisor to the government in Tehran in the 1970s.

“They will strike back one way or the other; I think chances of tensions becoming bigger is very, very high in the near future,” Fesharaki, who is now chairman of oil and gas consultancy Facts Global Energy, told.