Iran took extraordinary measures this spring to protect Foreign Minister Abbas Araghchi and parliament Speaker Mohammad Bagher Ghalibaf, assigning military escorts and making last-minute travel changes, the NYT reports.

The steps followed warnings the U.S. relayed through regional states that Israel might assassinate the two officials in the middle of negotiations.

In one incident, Ghalibaf's plane made an emergency landing in Mashhad after Iranian security forces flagged intelligence that Israel intended to attack the aircraft. According to the warning, two Israeli fighter jets had crossed into Iranian airspace near the border with Iraq.