Move comes after US said that no country would any longer be exempt from sanctions if it continues to buy Iranian oil.

Iranian legislators on Tuesday overwhelmingly approved a bill that labels all US military forces as “terrorist”, a day after Washington ratcheted up pressure on Tehran by announcing that no country would any longer be exempt from US sanctions if it continues to buy Iranian oil.

The bill is a step further from one last week that saw legislators approve labelling just US troops in the Middle East as “terrorist”, which was a response to the US designation of Iran’s Islamic Revolutionary Guard Corps (IRGC) as a “terrorist group” earlier this month.

US President Donald Trump‘s administration re-imposed sanctions on Iran, including on its energy sector, in November last year after pulling out of the landmark 2015 nuclear deal between Iran and world powers.

The US designation of the IRGC – the first-ever for an entire division of another government – added another layer of sanctions to the powerful paramilitary force, making it a crime under US jurisdiction to provide the guard with material support.

On Monday, the Trump administration announced it would not be extending sanctions exemptions for countries that import Iranian oil as part of its “maximum pressure” campaign that aims to eliminate Iran’s oil export revenue, which the US says funds destabilising activity throughout the region and beyond.

Hours before Trump’s announcement, Iran reiterated its long-running threat to close the Strait of Hormuz if it is prevented from using the crucial waterway in the Gulf, through which about a third of all oil traded at sea passes.

The US Navy has in the past accused Iranian patrol boats of harassing US warships in the waterway.

Iran’s foreign ministry promptly brushed off Trump’s move to stop the oil waivers, saying that Iran “basically has not seen and does not see any worth and validity for the waivers”.

But on Tuesday, 173 out of 215 legislators at the parliament session in Tehran voted for the new bill. Only four voted against while the rest abstained; the chamber has 290 seats.

The bill confirms Iran’s earlier label of the US Central Command, also known as CENTCOM, and all its forces as “terrorist”.

Any military and non-military assistance, including logistics support, to CENTCOM that can be detrimental to the IRGC will be considered a “terrorist” action, the semi-official ISNA news agency said.

The bill also demands the Iranian government take unspecified action against other governments that formally back the US designation. Saudi Arabia, Bahrain and Israel have all supported the Trump administration’s designation.

In addition, the legislators requested Iran’s intelligence agency provide a list of all CENTCOM commanders within three months so that Iran’s judiciary can prosecute them in absentia as “terrorists”.

The bill requires final approval by Iran’s constitutional watchdog to become law.

Other than underscoring Iran’s defiance, it is unclear what impact the bill could actually have, either in the Gulf or beyond.

The IRGC has forces and wields influence in Iraq, Syria, Lebanon and Yemen, and is in charge of Iranian missiles that have US bases in their range.

It is in charge of Iran’s ballistic missiles and nuclear programmes and answers directly to Supreme Leader Ayatollah Ali Khamenei. The force is estimated to have 125,000 personnel, comprised of army, navy and air units.

After the 1980s’ Iran-Iraq war, the IRGC also became heavily involved in reconstruction and has expanded its economic interests to include a vast network of businesses, ranging from oil and gas projects to construction and telecommunication.

The US State Department currently designates more than 60 organisations, including al-Qaeda and the Islamic State of Iraq and the Levant (ISIL or ISIS), Hezbollah and numerous armed Palestinian groups, as “foreign terrorist organisations”.