COPENHAGEN, Denmark - Police in Denmark and Sweden said they thwarted a terrorist attack possibly hours before it was to begin Wednesday, arresting five men they say planned to shoot as many people as possible in a Copenhagen building housing the newsroom of a paper that published cartoons of the Prophet Muhammad.

Four suspects were arrested in the suburbs of Copenhagen, including a Tunisian, a man from Lebanon and an Iraqi asylum-seeker. A fifth suspect, a Swedish citizen of Tunisian origin, was arrested in Sweden. The Danish intelligence service said it seized a submachine gun, a silencer and ammunition.

"An imminent terror attack has been foiled," said Jakob Scharf, head of the Danish Security and Intelligence Service, or PET. Scharf said three of the men were arrested as they left a suburban Copenhagen apartment, "either heading out to carry out the terror attack or to do some kind of reconnaissance."

Scharf described some of the suspects as "militant Islamists with relations to international terror networks." He said more arrests were possible.

Authorities said the arrests followed months of surveillance. Anders Danielsson, the head of Sweden's security police, said officers followed a car rented by three of the suspects from Stockholm to the Danish border late Tuesday or early Wednesday.

"We knew that there were weapons in the car," Danielsson said.

Danish intelligence said the group had been planning to enter the building where the Jyllands-Posten daily has its Copenhagen newsdesk and "to kill as many of the people present as possible."

Scharf said the assault was to have been carried out sometime before this weekend, and could have been similar to the 2008 terrorist attack in Mumbai, India, that left 166 people dead.

"It is our assessment that the plan was to try to get access" to the newspaper office and "carry out a Mumbai-style attack," Scharf told reporters.

Danish Justice Minister Lars Barfoed said the plot was "terrifying" and "probably the most serious terror attempt in Denmark." Scharf, however, said there was no need to raise the nation's terror threat alert level.

Danish intelligence said it arrested a 26-year-old Iraqi asylum-seeker living in Copenhagen and the three Swedish residents who had rented the car: a 44-year-old Tunisian, a 29-year-old Lebanese-born man and a 30-year-old whose national origin was not immediately released. The Danish resident was arrested in a separate raid, in a different Copenhagen suburb, from the other three, Scharf said.

Police evacuated a two-story apartment block where the Iraqi lived and were investigating an unidentified suspicious item found there, said PET and one resident, Birhe Kristensen.

The four men face preliminary charges of attempting to carry out an act of terrorism. A custody hearing was scheduled for Thursday. Police in Denmark do not release the names of suspects.

In Sweden, police said they arrested a 37-year-old Swedish citizen of Tunisian origin living in Stockholm.

"I am shocked that a group of people have concrete plans to commit a serious terrorist attack in this country," Danish Prime Minister Loekke Rasmussen told reporters. "I want to stress that regardless of today's event it remains my conviction that terrorism must not lead us to change our open society and our values, especially democracy and free speech."

The alleged plot follows several attacks and threats connected to 12 cartoons depicting the Prophet Muhammad published by the Jyllands-Posten in 2005 as a challenge to perceived self-censorship. The cartoons also provoked massive and violent protests in early 2006 in Muslim countries after the drawings were reprinted in a range of Western media. Islamic law generally opposes any depiction of the prophet, even favorable, for fear it could lead to idolatry.

Zubair Butt Hussain, a spokesman for the Muslim Council of Denmark, called the alleged plot "extremely worrying."

The organization "absolutely condemns any act of terrorism regardless of the motives and motivations that may lie behind," Hussain said.

Kurt Westergaard, the artist who drew the most contentious of 12 cartoons, said the foiled plot was "a direct attack on democracy and freedom of press."

"We may not and won't let anyone forbid us to criticize radical Islamism. We may not be intimidated when it comes to our values," Westergaard told the German tabloid Bild.

In January, a Somali man broke into Westergaard's home wielding an ax and a knife but the artist escaped by locking himself in a safe-room in the house. In 2008, two Tunisians with Danish residence permits were arrested for plotting to kill him.

In September, a man was wounded when a letter bomb he was preparing exploded in a Copenhagen hotel. Police said it was intended for the Jyllands-Posten, which also has been targeted in a number of thwarted terror plots in Norway and the United States.

U.S. citizen Tahawwur Rana faces trial in Chicago in February in connection with the 2008 terrorist attacks in Mumbai and a planned attack on the Jyllands-Posten.

In 2008, the Danish Embassy in Islamabad, Pakistan, was targeted by a car bomb that killed six people outside the mission.

The attacks and threats have caused concern and unprecedented security measures in Denmark, a country that prides itself on personal freedom and openness.

The JPPOL media group building, which includes Jyllands-Posten, is protected by metal fences and guards at all entrances. Mail is scanned and newspaper staff need identity cards to enter the buildings and the various floors.

Lars Munch, JPPOL chief executive, said his workers are worried.

"It is appalling for our group, for our employees and their families to see their workplace threatened," Munch said.

Hours after news of the arrests, Denmark's Crown Prince Frederik arrived at the JPPOL building for a previously agreed engagement.

"I wouldn't stand here if it had been a threat against me," Frederik told Danish TV2. Asked whether he was afraid, the heir to the throne replied "no," before entering the building to attend a sports award ceremony.

Denmark, with an estimated 207,000 Muslims among its 5.5 million people, has a minority nationalist party that has helped impose curbs on immigration. An estimated 300,000 Muslims live in Sweden, a predominantly Christian but secularized country of 9.35 million people that doesn't have nationalist movements of prominence.

Associated Press writer Louise Nordstrom contributed to this report from Stockholm.