A gunman was arrested hours before the start of a recent summit in the Bulgarian capital of countries wanting to join NATO, senior police officials said Saturday.

The man, whose identity was not disclosed, was arrested late Thursday near the Hilton hotel in downtown Sofia, Interior Ministry official Boiko Borisov told reporters.

Borisov said that the man carried a Scorpion automatic gun with a silencer. A policeman was seriously wounded during the arrest.

Presidents of East European and Baltic countries aspiring to join NATO met for a one-day summit Friday in the Bulgarian capital. Of the 10 presidents attending — Bulgaria, Estonia, Lithuania, Latvia, Romania, Macedonia, Albania, Croatia, Slovenia, Slovakia — eight were accommodated at the Hilton.

According to Borisov, four of those were a possible target.

Separately, Gen. Dimitar Vladimirov, head of the National Security Service, said in an interview on state radio that he had received information from "abroad" that one of the presidents might be an assassination target.

"Because of security reasons he was accommodated at another more secure place," Vladimirov said without naming the president, nor the place where he stayed.

Borisov refused to reveal any details on the identity or nationality of the suspect, saying that could prejudice investigations.

Bulgaria, like other European countries, has increased security in the wake of the Sept 11 terrorist attacks in the United States.

Declaring solidarity with the West in the war on terrorism, the leaders of 10 Eastern European and Baltic countries urged NATO on Friday to expand its military alliance and tighten security across the continent.

Meeting under heavy security at Bulgarian President Petar Stoyanov's residence, the heads of state said the Sept. 11 attacks underscored the need to bring their nations into NATO and present a more united front to terrorist elements.

Friday's summit ended with a solemn statement that "our governments will fully support the war against terrorism.

"The lesson we draw from the terrorist attacks in the United States is that the security of America and Europe is more intertwined than ever before," the statement continued. "The new democracies of Europe can help counter terrorist and criminal threats to the community of the West."

In a message to the Sofia conference, President Bush said the U.S. supported NATO membership "for all of Europe's new democracies -- from the Baltics to the Black Sea — who share our values.

"Your determination to stand side by side with the United States and the NATO alliance during this hour of trial sends a powerful message against the tyranny of terror," Bush said.

Stronger relations with emerging democracies are essential to counter the terrorist threat in Afghanistan, NATO Secretary-General Lord Robertson said.

"Afghanistan is a safe haven for terrorists precisely because it does not have a viable state structure. It is a black hole," he said. "That is why NATO is engaged in southeast Europe — to prevent such black holes from emerging on our doorstep. ... The new democracies have demonstrated once again that they are not just fair-weather friends."