DEVELOPING: Commandos backed by armored vehicles stormed a upscale restaurant in the Bangladesh capital’s diplomatic zone early Saturday, killing at least six Islamist militants who had taken dozens of hostages the previous evening.

Approximately three hours after the raid began, police Lt. Col. Tuhin Mohammad Masud confirmed to the Associated Press that the restaurant’s main building had been cleared and at least 13 hostages had been rescued.

Masud added that some of the militants had been captured and noted “the operation is still going on.” He also said there were casualties among the hostages, but declined to elaborate. 

Earlier, a police official told AP that that five bodies were seen lying in pools of blood at the restaurant. It was not immediately clear whether they were the remains of militants or hostages.

The Islamic State (ISIS) group claimed responsibility for the attack in Dhaka’s Gulshan area, according to the SITE Intelligence Group, which monitors jihadist activity online. The ISIS-affiliated Amaq news agency claimed that 24 people had been killed and 40 wounded, according to SITE, though those figures could not be independently confirmed. 

Amaq also posted photos purportedly showing the bodies of hostages. The authenticity of the pictures could not be confirmed either.

It was unclear how many hostages remained in the restaurant when the operation began at 7:40 a.m. local time (9:40 p.m. ET Friday). Local media reported that an Argentine and two Bangladeshis were rescued early Saturday, but details about their condition were not immediately available. 

Masud said those rescued in the raid included a Japanese national, who was injured, and two Sri Lankans.

The gunmen entered the restaurant at about 9:20 p.m. local time Friday, holding customers and staff at gunpoint. Kitchen staffer Sumon Reza, one of at least 10 people who managed to escape via the building’s roof, said at least 35 people, including 20 foreigners, were trapped inside.

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

Police said two officers died at a hospital after being wounded in a gun battle with the attackers, who also hurled bombs. Another 26 people were wounded, 10 of whom were listed in critical condition and six of whom were on life support, according to hospital staff. The injuries ranged from broken bones to gunshot wounds. Only one civilian was among the wounded.

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

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 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 ISIS, 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 ISIS claim, but could not confirm its authenticity.

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. ISIS and and Al Qaeda 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.

The Associated Press contributed to this report.