The U.S. launched fresh airstrikes against Iranian targets Tuesday, raising fears of a broader return to hostilities as Tehran threatened to choke off Gulf oil exports and escalating tensions rattled global energy markets and launched retaliatory strikes.

U.S. Central Command (CENTCOM) said American forces began striking targets belonging to Iran’s Islamic Revolutionary Guard Corps (IRGC) at noon ET (4 p.m. GMT).

CENTCOM said the operation followed recent attempted IRGC attacks against commercial shipping in the Strait of Hormuz and U.S. military personnel deployed in the region.

Iranian state media reported explosions on Qeshm Island, located along the northern side of the strategic waterway. The state-linked Nour News also reported explosions in the southern port cities of Bandar Abbas and Chabahar.

The strikes came after a weekend exchange of direct attacks between Washington and Tehran, the first since July, raising questions over whether a conflict that had increasingly shifted toward sanctions, blockades and economic pressure was again entering a more intense military phase.