Britain on Monday vowed more reprisals against what it said was Tehran's "weakened and isolated regime" after it executed a UK-Iranian dual national.
Following the killing of Alireza Akbari, the UK summoned Iran's most senior diplomat and recalled its own ambassador.
But despite slapping sanctions on Iran's prosecutor general Mohammad Jafar Montazeri it stopped short of opposition demands to ban the Islamic Revolutionary Guard Corps (IRGC).
Faced with more such demands in parliament, Foreign Secretary James Cleverly said he could not comment on future proscriptions.
But he said: "We do not limit ourselves to the steps that I have already announced."
And Prime Minister Rishi Sunak's spokesman told reporters: "We are reviewing further action with our international partners."
British MPs voted last week in favour of adding the IRGC to a list of banned terrorist organisations in the UK.
But the government is wrestling with the fate of other dual nationals held by the Islamic regime, and with the strategic aim of restoring an international nuclear pact with Iran.
Cleverly was nevertheless outspoken in denouncing Iran's leadership after Akbari, 61, was hanged allegedly for spying on Britain's behalf.
He told MPs that "we are witnessing the vengeful actions of a weakened and isolated regime, obsessed with suppressing its own people, debilitated by its own fear of losing power and wrecking its international reputation".
"Our message to that regime is clear: the world is watching you and you will be held to account, particularly by the brave Iranian people, so many of whom you are oppressing and killing."
Iran's foreign ministry spokesman Nasser Kanani said on Twitter that the execution was Tehran's response to "the United Kingdom's action in violating the national security of the Islamic Republic of Iran".
He added that the "noise of the British regime and the support of some human rights claimants in Europe from London show their lawlessness and illegality".
