Iran, locked in a worsening political standoff with Western powers, has handed down death sentences to several nationals accused of being part of a CIA-trained spy network uncovered earlier this year, an official said on Monday.

Seventeen people were arrested in all, a senior intelligence official told foreign media in Tehran. None of the suspects is a dual national, according to the official, who declined to be identified and didn't say how many were sentenced to death.

The announcement marks a show of force by Iran at a time of turbulent ties with the U.S. after the Trump administration withdrew from a 2015 nuclear accord with the Islamic Republic and reimposed crippling sanctions on its economy.