A spokesman for the Interior Ministry said yesterday that four anti- terrorist specialists from Germany had arrived in Vienna. At the same time, however, he warned that more attacks could be on the way.
Austrians were put on a state of alert over the weekend after three people were injured in two letter bomb explosions on Friday in the city of Linz and the nearby Bavarian city of Munich. Anxieties rose further on Tuesday after a letter bomb mailed from Austria went off in the north German city of Lubeck, injuring a politician.
All three bombs in the latest wave have been claimed by an Austrian-based underground group calling itself the Bavarian Liberation Army (BBA). This group has also claimed responsibility for two other waves of letter bomb attacks in December 1993 and October 1994 and the killing of four gypsies in a bomb attack this February. The BBA sees Austria as an integral part of a greater Germany - in common with all far-right extremist groups in both countries. It is also virulently xenophobic.
Friday's letter bombs were directed against a dating agency based in Linz that specialises in pairing east European women with Austrian men and an Austrian-born television presenter of German-Ghanaian parentage who lives in Munich.
Tuesday's bomb was addressed to Lubeck's deputy mayor, Dietrich Sazmeit, a critic of the mild sentences given to four right-wing extremists convicted of firebombing a synagogue in Lubeck in 1994.
The targeting of people known for their pro-foreigner, or racially tolerant, attitudes is in keeping with the pattern established in the previous bombings. According to Austrian experts on right-wing extremists, it also marks a radical departure for such groups.
"The people behind the letter bombs are quite different to the more common neo-Nazi thugs who hurl firebombs at asylum-seekers," said Wolfgang Neugebauer, of Vienna's anti-Fascist Documentation Centre. "Their methods are much more sophisticated. And instead of going for foreigners, they are going for people who are simply friendly towards foreigners."
In a letter purportedly sent by the BBA to Profil magazine, the organisation has drawn up a hitlist of 10 leading Austrian politicians, musicians and television personalities. All those mentioned on the list have so far said they will refuse to be intimidated. According to Mr Neugebauer, failure to capture those behind the bombs could lead to some form of self-censorship. "People may want to be a little more careful about what they say in future - particularly in public," he said.
Although very little is known about the BBA, officials in Vienna believe it has a very limited membership of technically skilled people who are probably in their fifties. In a bid to calm criticism of the police's failure to capture those responsible, Caspar Einem, the Austrian Interior Minister, earlier this week described the group as "extremely intelligent assailants who have yet to make any mistakes ... that is why the investigation has been so difficult."
In addition to calling in German investigators, Mr Einem said Austrian scientists and technicians would be enlisted to help in a special task force to be set up for the investigation.