Police arrested a Norwegian dressed as a police officer for the bombing in Oslo that killed seven and for a mass shooting at a Labor Party youth camp outside the capital that killed at least nine.

Update at 6:46 p.m. ET: A police official tells the Associated Press that today's terror is more like the 1995 Oklahoma City bombing by Timothy McVeigh than the Sept. 11, 2001, attacks on the World Trade Center by Islamist fundamentalists.

More AP updates here.

Update at 6:40 p.m. ET: Witnesses on Utoya have estimated that 20 to 30 people were shot dead, the English-language Nordic Page says. Hundreds of youths were on the island and had gathered to discuss the earlier bombing in Oslo when the gunman opened fire.

Update at 6:26 p.m. ET: The suspect is 32 years old and is talking with police, but he has not been charged.

"There is a dialogue between our investigators and the arrested," said Acting Police Chief Sveinung Sponheim, according to a translated article in Aftenposten. "He is willing to have a dialogue with the police. We have not yet received any kind of motive."

He confirmed that the gunman used automatic weapons in the island attack and that explosives were found there.

Update at 5:14 p.m. ET: Norwegian Prime Minister Jens Stoltenberg says police believe the death toll from the youth camp mass shooting is expected to exceed 10. So far, police have said nine or 10 died.

Update at 5:07 p.m. ET: The suspect is not affiliated with any terrorist organization, the Aftenposten newspaper in Oslo reports. Police "know the arrested man's identity, but will not provide more details about the arrest," according to Google's English translation of the article.

Police are not saying more about the suspect or his background.

Update at 4:40 p.m. ET: A suspect identified as Norwegian and dressed in a police uniform has been arrested, the head of Norway's national police says, according to Norwegian media.

"We believe he had dealings at both events," Acting Chief Sveinung Sponheim said, the newspaper Aftenbladet reports.

One witness told broadcaster NRK the gunman used shotguns, handguns and automatic weapons in the attack at the political youth camp.

In Washington, President Obama condemned the attacks and offered condolences to the Norwegian people, our colleagues at The Oval tell us.

Update at 4:02 p.m. ET: Oslo police report nine or 10 deaths from the shooting attack at the Labor Party youth camp on the island of Utoya. The gunman was seen in Oslo before the bomb blast.

By Douglas Stanglin

USA TODAY

Update at 3:14 p.m. ET: The New York Times quotes a terrorism expert as saying the terror group Ansar al-Jihad al-Alami, or the Helpers of the Global Jihad, issued a statement claiming responsibility for the attack. The newspaper quotes Will McCants, a terrorism analyst at CNA, a research institute that studies terrorism, as saying the group called the attacks a response to Norwegian forces' presence in Afghanistan and to unspecified insults to the prophet Mohammed. The statement said, "There is more to come." The Times notes that the claim could not be confirmed.

Update at 2:38 p.m. ET: An eyewitness tells Norway's NRK broadcaster he saw more than 20 bodies at the youth camp shooting, the Associated Press reports.

Update at 2:35 p.m. ET: Prime Minister Jens Stoltenberg urges Norwegians not to give in to fear in response to the bombing in central Oslo and the shootings at a youth camp outside the capital. The prime minister told Norwegian broadcaster NRK, "Co-workers have lost their lives today. … It's frightening. That's not how we want things in our country. But it's important that we don't let ourselves be scared because the purpose of that kind of violence is to create fear."

He says he's received unconfirmed reports of dead and injured at the camp shooting but details were sketchy.

Update at 2:26 p.m. ET: The BBC reports that Norwegian Prime Minister Jens Stoltenberg called an emergency crisis meeting of his government tonight.

Update at 2:01 p.m. ET: Police say at least seven people were killed in the blast in central Oslo, the Associated Press reports.

Update at 1:56 p.m. ET: There are conflicting reports on casualties at the youth camp shooting outside Oslo. Reuters initially quoted TV2 as saying several people were killed on the island of Utoya, where the shooting occurred. Reuters now quotes police as saying they cannot confirm deaths in the shootings.

Update at 1:46 p.m. ET: CNN quotes NRK state TV as saying police have "good reason" to believe that the bombing in central Oslo and the shooting at the youth camp are linked.

Update at 1:42 p.m. ET: A spokesperson for one Oslo hospital tells the BBC that 11 "heavily injured" people, suffering head and chest wounds, have been hospitalized and that at least 100 people have been treated for lesser injuries.

Update at 1:39 p.m. ET: Reuters quotes Norwegian police as saying they fear there may be explosives at a Labor Party youth camp where a gunman wearing a police uniform opened fire.

Update at 1:11 p.m. ET: NRK state TV reports that one person has been arrested at a Labor Party youth camp outside Oslo where at least five people were injured when a man wearing a police uniform opened fire.

Update at 12:54 p.m. ET: The French news agency AFP quotes a police office in Oslo as saying, "It is necessary to avoid big gatherings, to go back home. It is wise to stay at home."

Update at 12:46 p.m. ET: NRK state TV reports that five people were injured in the shooting at the youth camp run by the Labor Party on an island outside Oslo.

Update at 12:44 p.m. ET: The BBC reports that anti-terrorist police have been dispatched to an island about 40 minutes from Oslo where a man disguised as a policeman reportedly fired at a youth camp operated by the Labor Party. The BBC says Prime Minister Stoltenberg had been scheduled to address the gathering Saturday and was not there at the time of the shooting.

Update at 12:37 p.m. ET: In a separate incident that may be related, a Norwegian newspaper reports that a man in a police uniform fired at a youth camp outside Oslo. The BBC says Prime Minister Jens Stoltenberg had been scheduled at speak at the camp.

Update at 12:34 p.m. ET: The AP reports that at least 15 people were injured in the blast. Neither Prime Minster Jens Stoltenberg nor any government ministers were among the injured, the AP reports.

Update at 12:28 p.m. ET: Oslo police say the office of broadcaster TV2 has been sealed off because of a suspicious package, the AP reports.

Update at 11:13 a.m. ET: NRK state TV reports two people were killed in the explosion.

Update at 11:08 a.m. ET: The Norwegian newspaper VG says police confirm that several people were killed in the blast. Police say the explosion was the result of a bomb, VG reports.

Update at 10:56 a.m. ET: NRK state TV reports one person has been confirmed dead in the blast. Although the cause of the blast is unclear, NRK video shows a blackened car lying on its side amid the debris.

Update at 10:45 a.m. ET: Witness Ole Tommy Pedersen tells the AP that the blast shattered almost all the windows in a multistory highrise, sending a cloud of smoke billowing from the lower floors.

"I saw three or four injured people being carried out of the building a few minutes later," Pedersen says.

The AP reports that a Norwegian prosecutor filed terror charges this week against an Iraqi-born cleric for threatening Norwegian politicians with death if he is deported from the country. The indictment centered on statements that Mullah Krekar — the founder of the Kurdish Islamist group Ansar al-Islam — made to various media, including the American network NBC.

Update at 10:31 a.m. ET: Aftenposten reports that people warn there could be other bombs in the area.

Update at 10:28 a.m. ET: Aftenposten reports that most of the injuries were caused by shards of glass that struck people in the street when the explosion occurred around 3:30 p.m. local time.

Update at 10:22 a.m. ET: A video of the aftermath of the blast shows rubble covers several blocks in front of the buillding in downtown Oslo.

Update at 10:14 a.m. ET: Although the source of the blast is unclear, Al-Jazeera TV notes that Norwegian prosecutors on Tuesday filed a terrorism charge against Mullah Krekar, founder of the Kurdish Islamist group Ansar al-Islam. Mullah Krekar is accused of threatening a former minister, Erna Solberg, with death, Al-Jazeera says.

Update at 10:12 a.m. ET: Norwegian Prime Minister Jens Stoltenberg is safe, the Norwegian news agency NTB reports, according to the Associated Press.

Update at 10:09 a.m. ET: Reuters says PM Stoltenberg is safe after a blast that rocked central Oslo and knocked out windows in government buildings.

Update at 10:03 a.m. ET: Reuters reports at least eight people were injured in an explosion that knocked out most of the windows in a 17-story building where Prime Minister Jens Stoltenberg's office is located. The nearby oil ministry is reportedly on fire.

Update at 9:57 a.m. ET: A photograph of the scene on the Aftenposten website shows several blocks strewn with rubble and almost all the windows of one building shattered.

Update at 9:52 a.m. ET: The Norwegian newspaper Aftenposten quotes witnesses as saying Oslo's Market Street is "full of chaos" with people "running around bewildered," some with blood on their faces and hands. "You can smell the sulfur fumes," the newspaper's reporter says.

Update at 9:44 a.m. ET: The Associated Press reports that an explosion has damaged buildings in downtown Oslo; offices are being evacuated.

Original post: An explosion in Oslo today has blown out most of the windows of a government building housing the Norwegian prime minister's office, according to a witness, Reuters reports.

The news agency says several people have been injured.