Up to four letter bombs were sent to the European Parliament but only one exploded and no one was hurt, officials said on Monday.
There was immediate speculation of a link with a string of letter bombs sent last month from Italy to other European figures and institutions.
The bomb that went off was sent to Hans-Gert Poettering, head of the largest political group in the parliament, and was opened by a female employee early on Monday, a spokesman for Poettering's European People's Party said.
"It caught fire, there was a bang. Nobody was hurt," Robert Fitzhenry told Reuters.
Up to three other letter bombs failed to explode, the spokesman for the president of the parliament said.
"We understand that at least two or three packages have arrived but these other packages have not been opened and are being checked by parliamentary security," David Harley told Reuters.
"The other packages were all postmarked Bologna and posted on December 22," he said.
One of them was addressed to a Spanish deputy of the European People's Party, Jose Ignacio Salafranca Sanchez-Neyra, Harley said.
It was not immediately clear when the packages arrived. European Union institutions have been closed for a Christmas and New Year break, and Harley said they had arrived during the last few days.
A series of letter bombs were sent to European officials late last month. Investigators are looking at the possibility Italian anarchists are behind the mailings.
Harley said the bomb that went off in Poettering's office "sounded very like the one sent to Prodi's home".
A Reuters reporter at the parliament saw a bomb disposal truck and two fire engines outside the building on Monday, but said there was no other sign of increased security or police presence at the scene.
Chief European Commission spokesman Reijo Kemppinen, speaking about the wave of letter bombs shortly before the news of the device at Poettering's office was confirmed, said security was sufficient.
"Whatever security arrangements have been taken, they are necessary and they are sufficient and at the moment we are confident that everything that needs to be done has been done," he told a briefing.
LONDON: A letter bomb sent from Italy burst into flames in the Manchester office of a senior British Labour legislator in the European Parliament on Monday, his office said.
No one was hurt but the office of Gary Titley, leader of the British Labour party MEPs, was filled with smoke, his spokesman told Reuters.
"It filled the office with dense, acrid smoke. Luckily, nobody was injured," said the spokesman, Roger Fellows.
The attack followed the sending of up to four letter bombs to the European parliament earlier on Monday, one of which exploded.