A vessel in the Strait of Hormuz, as seen from Musandam, Oman [Source: Reuters]

Iran and the United States exchanged intensifying fire on Thursday in a week-long escalation that has largely ‌unraveled last month’s truce, while Tehran disputed President Donald Trump’s claim that a U.S. citizen had been released.

For the first time since a memorandum of understanding paused fighting last month, the United States launched two big waves of air strikes in a single day on Wednesday, mostly on targets near Iran’s southern coast, and kept firing on Thursday.

In a statement, U.S. Central Command said U.S. forces began “a new wave of strikes against Iran for the sixth consecutive night to further degrade Iranian military capabilities” at 2 p.m. EDT (1800 GMT) or 9:30 p.m. in Tehran.

Tehran has countered with missiles and drones targeted at U.S. military bases ​in neighbouring states, including a barrage at a recently expanded air base in Jordan.

After Tehran resumed its blockade of the Gulf through the Strait of Hormuz, Washington again blockaded Iranian ports from Wednesday.

The U.S. military said it fired on ​a tanker near Iran’s Kharg Island, with Hellfire missiles hitting its smokestack.

On Thursday evening, U.S. projectiles struck Qeshm Island and near Bandar Abbas — home to Iran’s largest port and key navy and ⁠Revolutionary Guards facilities — both on the Strait of Hormuz. Several locations in Bandar Abbas were hit by projectiles at 9:35 p.m. local time, the semi-official Mehr news agency reported, attributing the attack to the “American enemy.”

Iran has signalled it could prod its Houthi allies ​in Yemen to close another key strait: the Bab al-Mandeb at the mouth of the Red Sea.

Sources told Reuters Iran had already told the Houthis to shut it if Washington carries out threats to attack Iran’s infrastructure.

The week of increasingly intense exchanges has tested the ​boundaries of the restraint both sides largely observed during four months of fighting before last month’s truce.

Yet even as the attacks escalated, Trump on Wednesday welcomed what he described as the release of a

U.S. citizen detained in Iran, identified by a human rights lawyer as Dena Karari, calling it a gesture of goodwill by Tehran.

On Thursday, however, Iran’s judiciary challenged that account, saying no American prisoner had been released or exchanged from Iranian prisons, according to state media.