An Iranian-American scholar whom Iran once accused of fomenting political unrest has been arrested by authorities there for the second time in two years, his family said Friday.

Security forces arrested Kian Tajbakhsh late Thursday, a family member told The Associated Press. The relative was in contact with Tajbakhsh's wife, who witnessed the arrest in Tehran.

There was no independent confirmation from Iranian authorities. The relative spoke to the AP on condition of anonymity because of concern that public comments could aggravate Tajbakhsh's situation.

The arrest comes amid high political tension in Iran. Tehran has seen massive demonstrations following disputed June 12 presidential elections.

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Opposition protests erupted again Thursday in the capital, with marchers chanting "death to the dictator."

In some places, clashes erupted as police fired tear gas and charged demonstrators with batons.

Tajbakhsh, a social scientist and urban planner, spent four months in prison in 2007 on charges of endangering national security. He denied the allegations.

In the new arrest, two people who identified themselves as Iranian security officials arrived at his residence in Tehran late Thursday, Tajbakhsh's family said.

The officials questioned him and his wife, and searched the residence for three hours, before taking him away along with two computers and other items.

The family said no information was given about where Tajbakhsh was taken.

Tajbakhsh was held by authorities in 2007 after being charged along with three other Iranian-Americans with endangering national security.

Then, he was a consultant with the Soros Foundation's Open Society Institute, an organization that Iran has accused of trying to undermine the Iranian government.

Tajbakhsh's family says he ended his association with the Open Society Institute after his earlier imprisonment

Iran's arrest of Iranian-American journalist Roxana Saberi in January on spying charges sparked tensions at a time that U.S. President Barack Obama was looking for openings to negotiate on Iran's nuclear ambitions.

Saberi was released in May ahead of the elections and returned to the United States.