Multiple American citizens were among those killed and injured during a weekend siege at Kabul's Intercontinental Hotel, a U.S. State Department official said Tuesday after the death toll in the deadly attack rose to 22.

“We can confirm that there were U.S. citizen fatalities and injuries," the State Department said in a statement to Fox News. "We offer our deepest condolences to the families and friends of those who were killed and wish for the speedy recovery of those wounded."

The exact number of Americans killed and injured were not immediately released.

At least 22 people died when Taliban militants in suicide vests stormed the hotel in the Afghan capital Saturday. Officials initially said 18 people had been killed.

The Afghan interior ministry official said 14 of those killed were foreigners and eight were Afghans. At least 11 people who died were employees of KamAir, a private Afghan airline, Afghan Interior Ministry spokesman Najib Danish said Sunday.

Details about the attack are still being investigated, but an Afghan official told Reuters the possibility the militants had inside help could not be ruled out.

“The security company is being questioned and it has to provide a lot of explanation,” the official added. “We can’t rule out the possibility the terrorists had inside help.”

More than 150 people were forced to flee the building while parts of the structure caught fire. Some people were seen escaping the building by climbing down tied-together bedsheets from the upper-floor windows. Afghan forces rescued others.

Vassilis Vassileiou, a Greek Kam Air pilot in the hotel during the attack, said he cut a mattress open and hid inside it.

“They were first killing Westerners and then laughing at the dead,” said Vassileiou, according to Reuters. “I was constantly hearing shouts, shots and bangs on the doors.”

Mohammad Humayun Shams, the telecommunications director of eastern Laghman province, who was visiting Kabul and staying at the hotel, said he was able to escape by jumping into a tree from a hotel window as the attackers roamed the hallways, killing people.

"It was the worst night of my life," Shams said, adding that, as he ran, he couldn't tell the attackers apart from the police because they were all wearing the same uniforms.

The U.S. State Department said the United States is sending "deepest condolences" to the families and friends of those killed and wishing the injured a speedy recovery.

The Associated Press contributed to this report.