Turkish authorities yesterday said a suspicious powder found in a letter addressed to the head of the top administrative court was not anthrax as initially suspected, the state-run Anatolian news agency said.

A laboratory that tested the substance determined it was not anthrax, which can cause serious or fatal illness in humans. The news agency did not say what the powder was.

The letter sent to Mustafa Birden, president of the Council of State, was spotted when it spilled its contents at the central post office in the capital Ankara, Anatolian said.

A post office spokesman confirmed an incident with suspicious powder had occurred, but declined to elaborate.

Mr Birden was the target of a 2006 assassination attempt when a gunman stormed a court building and opened fire on justices, killing one, the suspect said in his trial which is still ongoing, newspapers reported in October.

In the so-called Ergenekon trial, some 200 people are being prosecuted for involvement in an alleged ultra-nationalist plot to overthrow Prime Minister Tayyip Erdogan's government.