But pressed by Democratic Representative Brad Sherman on whether Iran was responsible for the deaths of Americans on September 11, 2001, Hook replied, “No”.

Hook insisted that any potential US military moves on Iran would be defensive, saying: “There is no talk of offensive action.”

After al-Qaeda extremists killed some 3,000 people in 2001, the US Congress authorised then president George W. Bush to go to war in Afghanistan, where the group’s leader Osama bin Laden had found shelter.

The authorisation has since been cited by administrations to justify operations in countries as diverse as Yemen and the Philippines where al-Qaeda militants are found to be present.

Pompeo, in his April appearance before a Senate committee, said there was “no doubt” of a connection between Iran’s Shiite clerical regime and al-Qaeda, which is militantly Sunni.

Iran is believed to have been the long-time base of Hamza bin Laden, the son of Osama bin Laden, although some experts believe Tehran may have been holding him as leverage to prevent attacks against Iran or to put pressure on regional rival Saudi Arabia.

Tensions have soared in recent weeks, with the United States seeking to end all Iranian oil exports and Washington pointing to Iran as the culprit in a series of attacks on tanker ships.

Hook insisted that the Trump administration’s “maximum pressure” campaign – which included pulling out of a denuclearisation accord still backed by the Europeans – was succeeding, pointing to financial difficulties faced by Iran’s militant allies such as Hezbollah and Hamas.

But Hook said Trump was serious in his appeals for negotiations with Iran, which reached the nuclear accord after extensive talks with the administration of his predecessor Barack Obama.

“No one should be uncertain about our desire for peace and our readiness to normalise relations should we reach a comprehensive deal,” Hook said.

“We have put the possibility of a much brighter future for Iran on the table and we mean it,” he said.

Hook said a future US-Iran accord would focus on four areas – Tehran’s nuclear program, ballistic missiles, support for extremist groups and detention of US citizens.

Iran claims to have arrested spies, dismantled ‘new’ CIA network

Iran’s leaders have dismissed dialogue with the Trump administration, questioning its sincerity and pointing to US officials’ comments gloating over economic difficulties in the country.

Representative Ted Deutch, the Democrat who heads the House subcommittee on the Middle East, said Trump’s policy was incoherent and had triggered an escalation from Iran rather than any desired outcome.

“It appears there is no process in place to reassess the assumptions underlying the administration’s policies,” he said.

“Rather than force Iran back to the negotiating table, the administration’s policy is increasing the chance of miscalculation, which then would bring the United States and Iran closer to a military conflict,” he said.