MOSCOW, July 5 (RIA Novosti) - An Iranian employee of the British embassy in Tehran will be charged with threatening national security over his alleged role in post-election riots, his lawyer said.

Hossein Rassam, 44, the top political adviser at the embassy, has been charged with "acting against national security", Abdolsamad Khorramshahi told reporters.

Rassam is one of nine employees of the embassy arrested a week ago in connection with the protests that followed the June 12 presidential election. Seven have so far been released.

British Foreign Secretary David Miliband said that one of the two remaining staffers is set to be released later on Sunday.

The British ambassador in Tehran "was told by the deputy foreign minister that the eighth person would indeed be released today, that the papers had been signed, that there would not be a court process or charges," Miliband was quoted by the BBC as saying.

"That leaves one more in custody and all of our efforts are now directed towards getting that person out."

The trial of Rassam is likely to further strain tensions between Iran and the West.

Iran's leadership accused the U.K. and other Western powers of inciting demonstrations that followed the controversial re-election of President Mahmoud Ahmadinejad.

According to official data, Ahmadinejad won the election with more than 24 million of 40 million ballots cast. The runner-up, Mir Hossein Mousavi, claimed the reelection of the hardline president was marred by numerous irregularities.

Ahmadinejad's landslide victory triggered a week of protests by Mousavi's supporters. Regional media reports said 20 people were killed in the post-election violence, Iran's most severe unrest since the 1979 Islamic Revolution.