Apparent attacks on two tankers in the Gulf of Oman on Thursday forced their crews to abandon ship and left one vessel ablaze, a month after four tankers were damaged in the same area, raising alarms about the security of a vital passageway for much of the world’s petroleum.

The early morning incidents, which two shipping companies involved and the White House described as attacks, elevated tensions in a region already unsettled by the escalating conflict between the United States and some of its allies, and Iran.

Frictions have become so intense that other nations have pleaded with all sides to stay calm rather than provoke an all-out war. On Wednesday, Prime Minister Shinzo Abe of Japan, who was visiting Iran and trying to bridge the gap between Iran and the United States, warned of the risk of stumbling into military conflict.

Read more: New York Times