Police detained seven suspects Friday in an anti-terrorism operation in three Dutch cities, including the capital, aimed at thwarting a suspected plot to attack politicians and a government building, officials said.

The chief suspect in the raids was Samir Azzouz (search), a 19-year-old Dutch national of Moroccan descent who was acquitted of terrorism charges earlier this year.

As part of the security operation to protect the politicians, about two dozen officers in riot gear closed entrances leading to both houses of parliament and the government's information service. The weekly Cabinet meeting, however, went ahead as scheduled.

The National Terrorism Combat Coordinator (search) boosted security at the Justice and Home Affairs ministries, the secret service and other government buildings as a precaution, a statement said, but it saw "no reason to increase the national terrorism threat level."

Police declined to give details about the raids. There were reports of gunfire in the streets, but that could have been the sound of flash grenades used to stun the suspects while conducting the raids.

Azzouz was alleged to be in the process of purchasing automatic weapons and explosives "probably to carry out an attack with others on several politicians and a government building," a prosecution statement said.

On Thursday, media reported renewed threats against members of parliament Ayaan Hirsi Ali and Geert Wilders, both outspoken critics of Islamic extremism. The two went into hiding for several months after a Muslim extremist killed Dutch filmmaker Theo van Gogh (search) on an Amsterdam street last year.

In the days after Van Gogh's Nov. 2 death, tensions ran high in the Netherlands, with more than a dozen arson attacks against churches, mosques and Islamic schools.

The suspects, ranging from 18 to 30 years old, were detained in The Hague, Amsterdam and Almere. They will be brought before an investigating judge Monday.

The arrests came just days after renewed threats against members of parliament Ayaan Hirsi Ali and Geert Wilders, both outspoken critics of Islamic extremism. Wilders filed charges earlier this week after receiving a threat.

In the days after Van Gogh's Nov. 2 death, tensions ran high in the Netherlands, with more than a dozen arson attacks against churches, mosques and Islamic schools.

In September, the Dutch government introduced a U.S.-style terrorism threat gauge. The Web site of the National Terrorism Combat Coordinator shows the country currently at the second-highest of four levels of danger.

Authorities have been on alert as the first anniversary of Van Gogh's death approached, fearing another attack.

In December, a major terrorism trial will begin against 13 alleged members of the so-called Hofstad terrorism network believed linked to Van Gogh's murder and failed plots to attack politicians.