NAIROBI (Reuters) – Gunmen blasted their way into a hotel and office complex in the Kenyan capital on Tuesday, killing at least 14 people and sending workers diving under desks from an attack claimed by Somali Islamist group al Shabaab.

Eight hours after the assault began at Nairobi’s upscale 14 Riverside Drive complex, a burst of gunfire was heard in the area, suggesting the situation was not yet under control.

Scores of people were still hiding inside the complex, a security source said. A mortuary worker told Reuters around midnight (2100 GMT) that 14 people were killed in the attack.

Interior Minister Fred Matiang’i had said at 11 p.m. that all buildings had been secured and scores of people evacuated from the scene. But he did not comment on the attackers’ whereabouts and said security forces were still “mopping up”. An hour after he spoke, the gunfire rang out. The power in the hotel was out, a Reuters journalist at the scene said.

Nairobi is a major expatriate hub, and the compound targeted contained offices of various international companies, in an echo of a deadly 2013 assault on a Nairobi shopping center in the same neighborhood.

“The main door of the hotel was blown open and there was a human arm in the street severed from the shoulder,” said Serge Medic, the Swiss owner of a security company who ran to the scene to help when he heard of the attack from his taxi driver.

Medic, who was armed, entered the building with a policeman and two soldiers, he said, but they came under fire and retreated. An unexploded grenade lay in the lobby, he said.

“One man said he saw two armed men with scarves on their head and bandoliers of bullets,” Medic told Reuters, as gunfire echoed in the background.

Kenya has often been targeted by al Shabaab, who killed 67 people at the Westgate shopping center in 2013 and nearly 150 students at Garissa university in 2015. Al Shabaab says its attacks are revenge for Kenyan troops stationed inside Somalia, which has been riven by civil war since 1991.

More than six hours after Tuesday’s attack began, many office workers were still holed up inside the complex as officers escorted small groups to safety, some with their hands in their air. Foreign security advisors at the site scrambled to make sure their clients were safe.

GUNFIRE AND EXPLOSIONS

Kenyan police chief Joseph Boinnet said the attack began around 3 pm with an explosion targeting cars outside a bank followed by a detonation from a suicide bomber in the hotel lobby. As he spoke, a Reuters reporter on the scene reported heavy gunfire, then an explosion shortly afterwards.

CCTV footage showed three attackers dressed in black running across the parking lot at 3:30 p.m. shortly followed by a fourth. At least two of the men were wearing green scarves in the close-up footage. One appeared to be wearing a green belt with grenades in it.

At least seven people were killed and 25 wounded, hospital officials and witnesses told Reuters. Two Kenyans in their early 30’s working with governance consultants Adam Smith International were among the dead, a family member said. Both had young families, she said.

A Spanish national was among the injured, a Spanish diplomat told Reuters.

The U.S. Embassy had “actively” offered assistance to local authorities, a State Department official said.

“We are working with the Kenyan authorities to determine if there are any U.S. citizens affected,” the official said, adding all American diplomats were safe.

A woman shot in the leg was carried out of the complex, and three men emerged covered in blood. Some office workers climbed out of windows. Many told Reuters that they had to leave colleagues behind, still huddled under their desks.

“There’s a grenade in the bathroom,” one officer yelled as police rushed out from one building.

Geoffrey Otieno, who works at a beauty salon in the complex, said he heard a loud bang from something thrown inside the building, then saw shattered glass.

“We hid until we were rescued,” he said.

Meanwhile, Simon Crump, an Australian who works for an international firm in the complex, barricaded himself inside a spare room with two other people. They waited there for about 2-1/2 hours for help to arrive, their minds racing.

“You’re hiding under a desk trying to figure out what’s going on, and you just don’t know, as there’s so much misinformation,” he said.

When soldiers finally reached the group, they instructed them to put their phones away and put their hands in the air as they made their way to safety.

INTERNATIONAL COMPANIES

Al Shabaab, which wants to overthrow the weak, U.N.-backed Somali government and impose strict Islamic law, quickly said it was responsible. “We are behind the attack in Nairobi. The operation is going on,” Abdiasis Abu Musab, the group’s military operations spokesman, told Reuters by telephone in Somalia.

According to its website, 14 Riverside is home to local offices of international companies including Colgate Palmolive, Reckitt Benckiser, Pernod Ricard, Dow Chemical and SAP, as well as the dusitD2 hotel, part of Thai group Dusit Thani.

Kenya is a base for hundreds of diplomats, aid workers, businessmen and others operating around east Africa.

The Australian embassy is across the road from the compound.

“I just started hearing gunshots, and then started seeing people running away raising their hands up and some were entering the bank to hide for their lives,” a woman working in a bank in the complex said, adding she heard two explosions.

Kenyan television featured appeals for blood from local hospitals and showed police cordoning off the route to ensure vehicles could move quickly. Red Cross ambulances ferried victims away.

Kenyan troops, concentrated in south Somalia, originally went into Somalia to try to create a buffer zone along the border. They are now part of an African Union peacekeeping force.

The attack took place as a Kenyan court prepares to sentence four men accused of aiding the Westgate mall attack.