UN Secretary-General Antonio Guterres on Thursday asked for maximum restraint after Iran shot down a US drone.

"He is very concerned about this latest development, about the shooting down of the drone," Guterres' spokesman Stephane Dujarric told reporters.

"It is important that all parties exercise maximum restraint and avoid any action that could inflame the situation," said the spokesman.

He said Guterres has warned against any escalation, and has stressed that the world cannot afford a major conflict in that area.

Iran said the drone, an RQ-4A Global Hawk, violated its airspace, while the United States said it was flying over international waters when it was shot down by Iran on Thursday.