Reuters: Bahrain has detained a former member of parliament on charges of financing militants, state news agency BNA said late on Sunday, the latest in a series of arrests of opposition figures.

The agency did not name the man but quoted the director of criminal investigations as saying he was held on Aug. 18 after returning from a trip to collect funds in Iran.

Leading Shi'ite Muslim opposition group Al-Wefaq said in a statement it had not heard from one of its senior members, Sheikh Hassan Issa, since he was detained on Aug. 18, though it did not confirm he was the man mentioned in the report.

Washington has criticised its ally Bahrain over the arrest and trial of several prominent opposition figures, including the head of al-Wefaq, Sheikh Ali Salman, and Ibrahim Sharif, former head of the secular National Democratic Action Society, known as Waad.

The Sunni Muslim-led island kingdom, which hosts the U.S. Fifth Fleet, has experienced sporadic turmoil since mass protests in 2011 led by majority Shi'ites demanding reforms and a bigger role in government.

Bahrain says the opposition has a sectarian agenda and is backed by Shi'ite power Iran, a charge Shi'ite groups deny. Waad is a secular leftist party run by both Sunnis and Shi'ites.

The director of criminal investigation said the detainee had collected donations from various sources, including participants in rallies, to give to suspects being sought by the authorities as well as "a terrorist group" knowing about its activities.

The charges he was facing amounted to "financial terrorism", the director was quoted as saying. "He said the name of the arrestee was mentioned in a number of terrorist cases, including the Sitra terrorist blast on July 28 that killed two policemen," BNA said.

Issa was elected in the 2010 parliamentary poll but resigned a year later during the protests.

Al-Wefaq leader Sheikh Salman was sentenced in June to four years in jail after he was convicted of inciting unrest. Sharif, who was freed on June 19 after serving more than four years of a five-year sentence, had been charged with advocating the violent overthrow of the government.

Sharif's trial is due to start on Monday.