The Pentagon says a U.S. Coast Guard ship fired warning shots at Iranian speedboats Monday as they approached U.S. Navy ships escorting a nuclear submarine through the Strait of Hormuz. It was the third encounter between U.S. and Iranian ships in the past month.

The naval tensions came as dozens of Democratic officials wrote to President Biden asking him to revive the 2015 nuclear agreement with Iran, from which former President Trump withdrew in 2018. The officials demanded the lifting of Trump-era sanctions, writing, “The only result has been a vastly expanded Iranian nuclear program, increased regional instability, near U.S.-Iran war on multiple occasions, and severe economic sanctions that have contributed to a dire humanitarian crisis inside Iran.”