Kuwait summoned Tehran's envoy to demand the release of four Kuwaitis arrested in southwestern Iran, the Kuwaiti Foreign Ministry said on December 16.
The ministry said it was "following up closely with Iranian authorities" to secure the release of the four nationals detained in the Ahvaz area, according to a statement carried by KUNA state news agency.
It said that the Iranian ambassador was handed a memorandum "demanding their release and allowing visitation" by Kuwaiti diplomats.
Kuwait said its embassy in Tehran has been in contact with Iranian authorities to find out the reason behind the arrest of its nationals. It did not say when the four were arrested.
Kuwait joined other Gulf states in pulling its ambassador out of Tehran in January, rallying behind regional powerhouse Saudi Arabia after the kingdom's embassy in Tehran was torched by protesters.
A Kuwaiti and an Iranian were sentenced to death in January by a court in Kuwait for spying for Iran and Lebanon's Shi'ite group Hizballah.