Kuwait's state minister for cabinet affairs, Sheikh Mohammad Abdullah Al-Sabah, who is also acting information minister, confirmed earlier on Thursday that Kuwait had taken diplomatic action against Iran.
"While rejecting the accusations, Iran expresses regret on measures taken by Kuwaiti officials amid tensions in the region and in such a critical condition; we expect Kuwait to act rationally instead of responding to pressures and worsening the tensions", Iranian Foreign Ministry spokesman Bahram Qassemi was quoted as saying by the Mehr news agency.
Kuwait will shut down Iran's cultural and military offices at the embassy and decrease the number of Iranian diplomats in the country, Anadolu Agency reported Thursday.
Iran has always showed a responsible behavior towards the regional countries, including Kuwait in hard days, he said, but at the same time added that Tehran reserves the rights to show proper reciprocal measures against the reduction in the number of the two countries' diplomatic staffs.
"Following the supreme court ruling on the case ... the government of Kuwait has made a decision to take measures, in accordance with diplomatic norms and the Vienna Convention, towards its relations with the Islamic Republic of Iran", said al-Sabah added. "[Kuwait said] Alireza Enayati, the Iranian ambassador, must leave", ISNA said.
The official offered no further details and Iran has denied any involvement in the cell or the case.
In August 2015, Kuwait said it had busted the 26-member cell and seized arms, ammunition and explosives from them.
Analysts have warned the crisis could break apart the six-nation Gulf Cooperation Council, whose members are Saudi Arabia, Bahrain, Kuwait, Oman, Qatar and the United Arab Emirates.
They received sentences ranging from a few years in prison to, in one case, the death penalty, though the latter sentence was later reduced to life imprisonment.