The Joint Maritime Information Center, a global body in the field of maritime security, said in a warning issued late on Tuesday that Houthis supported by the Islamic Republic were preparing to attack ships from positions near the Bab el-Mandeb Strait in the south of the Red Sea.

According to the center, sources close to the group said the Houthis had completed preparations for an attack, including the deployment of missiles and drones.

The warning came after the Houthis announced this week that they were blocking shipping linked to Saudi Arabia—a threat aimed at Saudi Arabia’s oil exports from the port of Yanbu. This route has become vital amid the near halt in traffic through the Strait of Hormuz.

However, the center added that in the past 48 hours, no confirmed attacks on commercial vessels had taken place and that ships continued to transit without disruption.