The chief of NATO has strongly urged Iran to refrain from taking any action that may lead to a cycle of retaliations.
Secretary General Jens Stoltenberg spoke to reporters in Brussels on Monday after an emergency NATO meeting.
The US ambassador briefed the alliance on the US drone attack that killed top Iranian general Qassem Soleimani in Iraq last Friday.
Stoltenberg said NATO members are united in condemning Iran's support of a variety of different terrorist groups in the Middle East, and are calling for restraint and de-escalation.
Stoltenberg said a new conflict would be in no one's interest, and pressed Iran to refrain from further violence and provocations.
NATO members also agreed to closely monitor Iran's nuclear development, after Tehran said it will step up its uranium enrichment activities in breach of limits set by a 2015 nuclear deal.
NHK
