Donald Trump said Friday that US forces have “obliterated” military targets on Iran’s Kharg Island and warned that the oil infrastructure there could be next.

“For reasons of decency, I have chosen NOT to wipe out the Oil Infrastructure on the Island,” Trump wrote on social media. “However, should Iran, or anyone else, do anything to interfere with the Free and Safe Passage of Ships through the Strait of Hormuz, I will immediately reconsider this decision.”

Within hours of Trump’s announcement, the Iranian armed forces said any attack on Iran’s oil and energy infrastructure will lead to attacks on energy infrastructure owned by oil companies cooperating with the United States in the region, Iranian media reported.

The small island in the Persian Gulf is the primary terminal through which Iran’s oil exports pass. Until Friday, the island had been spared during US and Israeli strikes on Iran.

Just a day before, the speaker of the Iranian parliament said such a strike would provoke a new level of retaliation. Mohammad-Bagher Ghalibaf warned in a Thursday social media post that attacks on the islands on Iran’s southern maritime frontier would cause Iran to “abandon all restraint”, underscoring how central they are to the country’s economy and security.

Trump announced the action as he prepared to fly to Florida for the weekend. The president answered questions from reporters traveling with him before he boarded Air Force One, but he did not mention the latest US military operation against Iran.

Axios reported last week that administration officials were weighing seizing the 5-mile coral island.

Experts told the Guardian earlier this week that military actions against Kharg Island are likely to increase oil prices, already surging since the war began on 28 February.

“We may see the $120 a barrel price we saw on Monday heading to the $150 if Kharg were attacked,” said Neil Quilliam of the Chatham House thinktank. “It’s too vital for global energy markets.”

Earlier Friday, a US official told the Associated Press that the American military had ordered 2,500 marines and the amphibious assault ship USS Tripoli to the Middle East.

Marine Expeditionary Units are able to conduct amphibious landings, but they also specialize in bolstering security at embassies, evacuating civilians and disaster relief. The deployment does not necessarily indicate that a ground operation is imminent or will take place.

The 31st Marine Expeditionary Unit, as well the Tripoli and other amphibious assault ships carrying the Marines, are based in Japan and have been in the Pacific Ocean for several days, according to images released by the military. The Tripoli was spotted by commercial satellites sailing alone near Taiwan, putting it more than a week away from the waters off Iran.

Earlier in the week, the navy had 12 ships, including the aircraft carrier USS Abraham Lincoln and eight destroyers, operating in the Arabian Sea. Should the Tripoli join this flotilla, it would be the second-largest ship behind the Lincoln in the region.

Associated Press and Reuters contributed reporting