An explosion outside the U.S. embassy in Oslo early Sunday caused minor damage but no injuries, and police say terrorism is a possible cause.

U.S. officials, including House Intelligence Chairman Rick Crawford, echoed concerns about threats to American embassies amid the ongoing U.S.-Israeli conflict with Iran.

Since Feb. 28, several U.S. embassies in the Middle East have been closed or placed on high alert after attacks, including drone strikes in Dubai and Riyadh.

Norwegian Prime Minister Jonas Gahr Støre called the Oslo blast “very serious and completely unacceptable,” though no suspects or motives have been identified, Politico has reported.

U.S. lawmakers, including Sen. Tim Kaine, said they are coordinating with the State Department to enhance security at diplomatic facilities worldwide.