Anglican bishops joined MPs and peers on Thursday in calling on the government to address atrocities against religious minorities in Iran.
Hundreds of people are imprisoned because of their faith in the Shia-led country according to human rights groups. Although officially free to practise their faith, Christians are frequently arrested if they gather to worship or convert away from Islam.
The former Bishop of Oxford John Pritchard was joined by MPs from different parties as well as members of the House of Lords.
He joined MPs and Peers calling for an independent investigation of a massacre of political prisoners in Iran in 1988.
In the summer of 1988, based on a fatwa decreed by the Islamic Republic's founder Ayatollah Khomeini, some 30,000 political prisoners were massacred in the space of a few months and buried secretly in mass graves. The officials responsible for the massacre currently hold some of the highest positions in the regime.
Pritchard said: "We must now focus on human rights abuses that are taking place in Iran."
The Bishop of Moray, Ross & Caithness, the Bishop of Croydon, the Bishop of Stepney and the former Bishop of Sodor and Man also attended to put pressure on the Foreign Office over the crackdown.
Rt Rev Jonathan Clark, Bishop of Croydon, told Christian Today the UK and US governments were "ignoring human rights issues" because the nuclear agreement and trade are "bigger fish to fry".
"They are ignoring the fact the Iranian government kills and tortures its own people," he said.
Human rights must be part of how the UK does diplomacy, he added.
Labour MP Jim Fitzpatrick also attended the meeting and urged the government to address the "completely unacceptable" cases of " discrimination against ethnic or religious minorities as well as the continuing use of the death penalty and restriction on freedom of expression".
He said: "I know that the UK Government has repeatedly raised concerns about human rights with the Iranian authorities, including the imprisonment of seven Bahá'í faith leaders who have been sentenced to 20 years in prison.
"I hope that the Government will continue to press Iran on these sensitive issues and urge much greater progress."
Tory MP Dr Matthew Offord said: "The current UK policy on pursing business opportunities in Iran in the post-nuclear deal era risks empowering the Revolutionary Guards, which is the paramilitary arm of the Supreme Leader and the major force in exporting terror out of Iran and suppressing any popular dissent."
