A Kuwaiti court sentenced two men to death on Tuesday on charges of spying for Iran and the Lebanese Shiite group Hezbollah.
One of the condemned, an Iranian citizen, was sentenced but not in police custody at the time of sentencing.
Eighteen other defendants involved in the same case received sentences ranging from five years to life imprisonment, while three others were acquitted.
The defendants had also been accused of attempting to carry out "hostile acts."
The sentences come just one week after Kuwait withdrew its ambassador from Tehran in protest after the Saudi embassy in Tehran was stormed by demonstrators.
The case began with the arrest in August of what the Interior Ministry said was a "terrorist cell" in farmland near the Iraqi border.
The ministry said large quantities of weaponry and explosives had been found on the scene.
Kuwait has somewhat better relations with Iran than its Sunni Arab Gulf neighbours.