US president Donald Trump has blamed Iran for attacks on oil tankers near the strategic Strait of Hormuz, but also expressed hope that implicit American threats to use force will bring the Islamic Republic back to the negotiating table.

Mr Trump’s claim comes as the Pentagon considers beefing up defences in the Persian Gulf.

A day after explosions blew holes in two oil tankers just outside Iran’s territorial waters, rattling international oil markets, the US administration seemed caught between pressure to punish Iran and reassure Washington’s Gulf Arab allies without drawing America closer to war.

“Iran did it,” Mr Trump told Fox News Channel’s Fox & Friends.

Hassan Rouhani Iranian president Hassan Rouhani (AP)

He did not offer evidence, but the US military released video it said showed Iran’s Revolutionary Guard removing an unexploded mine from one of the oil tankers targeted near the Strait of Hormuz, suggesting Tehran wanted to cover its tracks.

By pointing the finger at Iran, Mr Trump is keeping a public spotlight on an adversary he accuses of terrorism but has also invited to negotiate.

The approach is similar to his diplomacy with North Korea, which has quieted talk of war but not yet achieved his goal of nuclear disarmament.

Iran has shown little sign of backing down, creating uncertainty about how far the Trump administration can go with its campaign of increasing pressure through sanctions.

Iran denied any involvement in the attacks and accused Washington of waging an “Iranophobic campaign” of economic warfare.

Persian Gulf TensionsThe US military revealed damage and a suspected mine on the Kokuka Courageous in the Gulf of Oman (US Central Command/AP)

A US Navy team was aboard one of the tankers, the Japanese-owned Kokuka Courageous, collected forensic evidence.

Apparently alluding to the US video, Mr Trump said Iran’s culpability had been “exposed”.

He did not say what he intended to do about it but suggested “very tough” US sanctions, including efforts to strangle Iranian oil revenues, would have the desired effect.

Mr Trump added: “They’ve been told in very strong terms we want to get them back to the table.”

Just a day earlier, the US president took the opposite view, tweeting that it was “too soon to even think about making a deal” with Iran’s leaders. “They are not ready, and neither are we!”

Last year, Mr Trump withdrew the United States from an international agreement to limit Iran’s nuclear programme that was signed in 2015 under his predecessor, Barack Obama.

He has since then reinstated economic sanctions aimed at compelling the Iranians to return to the negotiating table. Last month, the US ended waivers that allowed some countries to continue buying Iranian oil, a move that is starving Iran of oil income and that coincided with what US officials called a surge in intelligence pointing to Iranian preparations for attacks against US forces and interests in the Gulf region.

On May 5, the US announced it was accelerating the deployment of the USS Abraham Lincoln aircraft carrier battle group to the Gulf region. It also sent four nuclear-capable B-52 bombers to Qatar and has beefed up its forces in the region by deploying more Patriot air defence systems.