Iran urged Bahrain on Wednesday to free Shiite opposition leader Sheikh Ali Salman who stands accused of seeking regime change by force in the Sunni-ruled Gulf state.
"We are extremely worried about his situation," foreign ministry spokeswoman Marzieh Afkham told reporters.
"We want him to be released," she said of Salman, head of the Shiite movement Al-Wefaq, which boycotted a parliamentary election in November having dismissed it as a farce.
"We believe that the security measures Bahrain's government has adopted to solve its internal issues are wrong," Afkham added.
Shiite Iran has been accused of interfering in Bahrain's affairs ever since its Sunni ruling family crushed month-long protests led by Al-Wefaq in 2011 seeking an elected government in the Shiite-majority kingdom.
Salman's detention, which came on Sunday two days after he was re-elected as party leader, sparked fresh clashes between his supporters and police in Shiite villages outside the capital Manama.
The prosecution said Monday that the 49-year-old cleric had been charged with "promoting regime change by force, threats and illegal means and of insulting the interior ministry publicly."
Salman is also accused of inciting people to break the law and of "hatred towards a segment of the people".
On Tuesday, officials said he would remain in custody for seven days.
Strategically located just across the Gulf from Iran, Bahrain is home to the US Navy's Fifth Fleet, and Britain announced plans earlier this month to build a naval base of its own there.
But authorities have repeatedly rejected Al-Wefaq's demand for an elected prime minister to replace the current government, which is dominated by the royal family.