The president's tweets may reflect the latest US intelligence. Pentagon officials confirmed yesterday that all US ships retain the right to self-defence.
Trump has adopted a much tougher approach to Iran than his predecessor Barack Obama, withdrawing the US from the 2015 nuclear deal.
The president has declined to lift hard-hitting sanctions readopted after leaving the deal despite the Covid-19 crisis, though has said he is open to giving aid to Iran.
It came as Iran's Revolutionary Guard dramatically unveiled a secret space programme, launching its first military satellite into orbit.
Experts said the move suggested that Iran no longer felt cowed by the "maximum pressure" campaign led by the US, which imposed the crippling economic sanctions.
"This raises a lot of red flags," said Fabian Hinz, a researcher at the James Martin Center for Nonproliferation Studies in California. "Now that you have the maximum pressure campaign, Iran doesn't have that much to lose anymore."
Mike Pompeo, the UMS secretary of state, said yesterday that Iran should be held accountable for having its military wing organise a satellite launch.
Earlier this month, the US said 11 vessels from the Iranian navy came close to their own ships in the Persian Gulf, calling the move "dangerous and provocative".
In June and May 2019 the US also blamed Iran for damaging several ships in the Persian Gulf. The Iranian regime then shot down a US surveillance drone as it flew over the Strait of Hormuz, which nearly led to an armed confrontation.
