Policemen secure the area in front of the Serbian Presidency building in Belgrade on Thursday, after a man with a hand grenade entered the Serbian president's headquarters and threatened to detonate the device. (Darko Vojinovic/Associated Press)

Serbian authorities disarmed a man threatening to blow himself up at the headquarters of the Serbian president on Thursday, a senior official said.

The man entered the building in the capital Belgrade late Thursday morning carrying two hand grenades. Police, who had taken one grenade from the man earlier, seized the second grenade after hours of negotiations, the BBC quoted a presidential office spokeswoman as saying.

It's not immediately clear how the police took control of the grenades.

Several office workers were believed to be in the building. President Boris Tadic entered the building shortly after the incident began, but officials say he was in no danger.

Jasmina Stojanov, Tadic's press office spokeswoman, said that negotiations between the man and Interior Ministry officials were ongoing.

The man, identified by one official as bankrupt businessman Dragan Maric, was seated in a small lobby at a side entrance, surrounded by shielded policemen pointing guns at him while negotiators tried to persuade him to surrender, Belgrade's independent B-92 radio said.

Maric had announced his plan in an email sent to various government addresses, the official said.

The man said in the email that he would blow himself up if a court did not rule in his favour in an unspecified case by 4 p.m. local time Thursday, the official said.

"Even death is better than tyranny," the man said in the email, according to the official, who refused to be named because she was not authorized to discuss the incident.

After the deadline passed, there was no sound from the building, which is in a park across from the parliament building.

Stojanov could not say what the man's motive was.

With files from The Associated Press