Punishing those behind the US killing of Iranian commander Qassem Soleimani is a “basic and definite principle” of Tehran’s foreign policy, Iran’s foreign ministry’s spokesman said on Monday.

“It is a definite principle in the foreign policy of the Islamic Republic of Iran that (those involved in the killing of Soleimani) must be brought to justice,” Iran’s official IRNA news agency quoted foreign ministry spokesman Saeed Khatibzadeh as saying.

“The basic principle in the foreign policy of the Islamic Republic of Iran was formed after the cowardly assassination of (Soleimani): The action taken by the perpetrators and advisers of this cowardly act will not go unpunished,” Khatibzadeh said.

Soleimani was killed in a US airstrike in Iraq on January 3, 2020, ordered by then President Donald Trump. Soleimani headed the Quds Force, the overseas arm of Iran’s Islamic Revolutionary Guard Corps (IRGC).

Iran has been routinely threatening revenge against Trump and members of his administration over the killing of Soleimani. The Associated Press reported in March that the US State Department spends more than $2 million a month to provide 24-hour security for former secretary of state Mike Pompeo and former Iran envoy Brian Hook, who face “serious and credible” threats.

Under President Joe Biden, the US has for over a year engaged in indirect talks with Iran in Vienna aimed at reviving the 2015 nuclear deal, which Trump abandoned in 2018.

The talks have been paused since last month, reportedly over an Iranian demand to have the IRGC removed from the US Foreign Terrorist Organization (FTO) list. The US designated the IRGC as a foreign terrorist organization under Trump in 2019.

Trump withdrew Washington from the nuclear deal in 2018 and reimposed sweeping sanctions on Tehran, saying the deal failed to address Iran’s ballistic missile program and regional activities and it did not block Iran’s path to a nuclear weapon.

Iran, which insists its nuclear program is for peaceful purposes only, responded by expanding its nuclear program, breaching most of the deal’s restrictions.

The 2015 deal offered Iran sanctions relief in exchange for curbs on its nuclear program. The Vienna talks, which began in April 2021, aim to bring Iran back into compliance with the deal and facilitate a US return to the agreement.