US Iran War: In the biggest declared wave of tit-for-tat attacks on shipping by both sides since the start of the six-month-old war, Iran said on Wednesday it had attacked 10 ships near the Strait of Hormuz after the US sank five Iranian oil tankers.

The attacks sent the price of oil surging, with the international Brent crude benchmark breaching $100 a barrel for the first time since July. At least one seafarer aboard a tanker was reported killed and another listed as missing.

Iran also said it had fired ballistic missiles at a base used by US forces in Jordan. Attacks by both sides since the end of Aug have shattered a month of relative calm.

The Revolutionary Guards said they would sharply escalate their response to any further attacks, and if the enemy struck two or three Iranian targets, Iran would respond by hitting 20.

The Americans said they destroyed five Iranian oil tankers overnight, releasing video of ships ablaze before they sank. The US military’s Central Command called its attacks a response to Iran’s Islamic Revolutionary Guard Corps targeting a US navy warship twice with ballistic missiles over the previous two days. No Americans were harmed, the US said. Washington has announced a new policy of attacking Iranian tankers in retaliation for fire that threatens its warships. Iran says it is using new, more capable missiles to attack US ships.

“Iran continues to try to hit US naval ships, and for every time they do that or try to do that, they’re going to lose tankers,” US secretary of state Marco Rubio told reporters during a visit to Colombia.

After Iran announced its strikes in response, saying it fired on two US ships and eight tankers, reports indicated vessels had been hit in waters near several neighbouring countries. One seafarer was killed aboard the oil products tanker Hercules Star while at anchorage off Dubai and another crew member was missing, the vessel’s charterer, Peninsula, said. Maritime security sources said it may have been hit by a drone.