President Donald Trump has blamed Iran for attacks on oil tankers near the strategic Strait of Hormuz, but he also held out hope that implicit US threats to use force will yield talks with the Islamic Republic as the Pentagon considers beefing up defenses in the Persian Gulf area.

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

"Iran did it," Trump said Friday on Fox News Channel's "Fox & Friends."

He didn't 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, Trump was keeping a public spotlight on an adversary he accuses of terrorism but also has 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.

A US Navy team on Friday was aboard one of the tankers, the Japanese-owned Kokuka Courageous, collecting forensic evidence, according to a US official who spoke on condition of anonymity to discuss a sensitive operation.

Apparently alluding to the US video, 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.

"They've been told in very strong terms we want to get them back to the table," Trump said.

Just a day earlier, the 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!"  Trump last year withdrew the United States from an international agreement to limit Iran's nuclear program that was signed in 2015 under his predecessor, President Barack Obama.