(AP) -- Heavily armed militants struck at the heart of Bangladesh's diplomatic zone on Friday night, taking dozens of hostages at a restaurant popular with foreigners. Two police officers were killed and at least 26 people wounded in a gunbattle as security forces cordoned off the area and sought to end the standoff.

The Islamic State group claimed responsibility for the attack on the Holey Artisan Bakery in Dhaka's Gulshan area, according to the SITE Intelligence Group, which monitors jihadis activity online. At least 35 people, including about 20 foreigners, were still trapped inside the restaurant, said kitchen staffer Sumon Reza, who was among more than 10 people who managed to run to the rooftop and escape.

The attack marks an escalation in the growing drumbeat of militant violence to hit the traditionally moderate Muslim-majority nation in the past three years, but with increasing frequency in recent months. Most attacks have been by machete-wielding men singling out individual activists, foreigners and religious minorities.

Bangladesh did not immediately respond to the claim of responsibility by IS, but in the past have denied that the extremist group has a presence in the country. The U.S. State Department said it had seen the IS claim, but could not confirm its authenticity.

More than eight hours after the hostage crisis began, a standoff had developed with little sign of any resolution.

The attackers "have not responded to authorities' calls for negotiation," said a member of the elite anti-crime force, Rapid Action Battalion, identifying himself as Lt. Col. Masood, during an interview with the Indian TV channel Times Now.

He said authorities were planning to launch a coordinated response at dawn, and that the security cordon would prevent any of the attackers from escaping. Authorities also ordered internet services to be blocked across the country, according to internet service provider Aamra.

Police said the two officers died at a hospital after being wounded in the gunfire with as many as nine attackers, who also hurled bombs. Ten of the 26 wounded were listed in critical condition, six of whom were on life support, according to hospital staff, who said the injuries ranged from broken bones to gunshot wounds. Only one civilian was among the wounded.

Reza said the attackers chanted "Allahu Akbar" (God is Great) as they launched the attack around 9:20 p.m. Friday, initially opening fire with blanks. A huge contingent of security forces cordoned off the area around the bakery.

Resident Lutful Amin told The Associated Press he heard several explosions, the last of which went off around 10:45 p.m.

The head of the Rapid Action Battalion told reporters Friday night that they were working to save the lives of the people trapped inside the restaurant. The hostages included an unknown number of foreigners.

Their nationalities were not immediately clear. On Saturday, Japan's top government spokesman Yoshihide Suga said at a hastily called news conference in Tokyo that the government is trying to confirm that Japanese were among the hostages. Prime Minister Shinzo Abe told reporters that saving lives is the top priority.

"Some derailed youths have entered the restaurant and launched the attack," Benazir Ahmed said. "We have talked to some of the people who fled the restaurant after the attack. We want to resolve this peacefully. We are trying to talk to the attackers, we want to listen to them about what they want."

"Our first priority is to save the lives of the people trapped inside," Ahmed said. He would not say how many people were being held hostage.

Among the hostages was a businessman and his wife and two children, according to his uncle Anwarul Karim.

"My nephew Hasnat Karim called me and said he was inside with his family. He told me, 'Please save us, please!' And he hung up," he said. "We do not know what is going on there."

In Washington, a White House official said President Barack Obama was briefed on the attack by his chief counterterrorism adviser Lisa Monaco. The president asked to be kept informed as the situation develops, said the official, who was not authorized to speak publicly about the president's meetings.

State Department spokesman John Kirby says the U.S. is in contact with the Bangladesh government and has offered its assistance to bring those responsible to justice.

He said all official American personnel are accounted for with no injuries reported, and the department is working with local authorities to determine if any U.S. citizens and locally-employed staff were affected.

The spree of recent attacks in Bangladesh have raised fears that religious extremists are gaining a foothold in the country, despite its traditions of secularism and tolerance.

About two dozen atheist writers, publishers, members of religious minorities, social activists and foreign aid workers have been slain since 2013. On Friday, a Hindu temple worker was hacked to death by at least three assailants in southwest Bangladesh. IS and and al-Qaida affiliates have claimed responsibility for many of the attacks.

Prime Minister Sheikh Hasina's government has cracked down on domestic radical Islamists. It has accused local terrorists and opposition political parties -- especially the main opposition Bangladesh Nationalist Party and its Islamist ally Jamaat-e-Islami -- of orchestrating the violence in order to destabilize the nation, which both parties deny.

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Associated Press writers Katy Daigle in New Delhi, Matthew Pennington in Washington and Ken Moritsugu in Tokyo contributed to this report.