(Adds comments from Canadian, Austrian police)

By Karin Strohecker

VIENNA, Sept 13 (Reuters) - Canadian police have arrested a fourth suspect in connection with three Austrians linked to al Qaeda who were detained in Vienna on Wednesday, the Austrian Interior Ministry said on Thursday.

Canadian police later said they had arrested Said Namouh, 35, in the town of Maskinonge in the French-speaking province of Quebec on Wednesday. He was charged on Thursday with plotting to cause explosions in a foreign country.

Austrian officials said the man had been in contact with the three arrested in Vienna, who are suspected of having posted a video message on the Internet threatening attacks on Austria and Germany.

"The man in Canada was arrested at the same time as the three in Vienna," said Interior Ministry spokesman Rudolf Gollia. "They communicated a number of times through online Internet forums and by e-mail."

Gollia said the suspect arrested in Canada was of African descent but declined to give any further details. Canadian police said Namouh -- arrested after a joint operation with Austrian authorities -- had posed no direct threat to Canada.

The three suspects held in Vienna are a 22-year-old man and his 20-year-old wife and another man of 26, all of whom are second-generation immigrants from Arab countries and hold Austrian passports.

The video message posted in March demanded German and Austrian soldiers leave Afghanistan, but in electronic surveillance over several months police found no concrete indications that attacks were in the offing, the ministry said on Wednesday.

The arrests come just over a week after Germany said it foiled an Islamist militant plan to carry out "massive bomb attacks" on U.S. installations in the country. Germany arrested three men.

The Austrian Interior Ministry said it knew of no links between the German and the Austrian suspects.

Austrian authorities said they decided to close in on the suspects after learning they were about to leave the country.

"We received some information that the main suspect and his newly wed wife were planning to leave the country and travel to Egypt for their honeymoon," said Gollia. "The second reason was that the main suspect said he would destroy his computer, and a lot of information would have been lost."

The suspect arrested in Canada had also been about to leave the country, Gollia added.

(Additional reporting by David Ljunggren in Ottawa, editing by Peter Galloway)

AlertNet news is provided by