Nairobi, Kenya CNN  — 

An evacuation of a hotel complex in the Kenyan capital Nairobi is still ongoing, hours after suspected Islamist extremists launched an attack killing at least 11 people, including a US citizen.

Tuesday’s coordinated assault by armed gunmen on the Dusit D2 compound, an upmarket cluster of shops and hotel facilities, represents the most high-profile terror attack in the East African country in several years.

Authorities reported that “scores” of Kenyans and foreign nationals had been evacuated from the compound, and that the site had been secured, but sporadic gunfire continued to be heard hours after the all-clear had been given.

A source at the hotel assisting with security called the death toll “conservative” and expected it to rise. “I saw six dead on the footpath exit over the river and five more at the secret garden cafe,” said the source. The US state department confirmed a US citizen was killed in the attack, but provided no further details.

A woman is escorted from the Riverside Drive complex in Nairobi.

Responsibility for the assault, described by police as a “suspected terror attack,” has been claimed by Somali Islamist militant group Al-Shabaab, according to the SITE Intelligence Group.

Across the capital Wednesday, friends and family of those believed to have been inside the compound during the attack waited nervously to be reunited with their loved ones. The Red Cross has asked families to call into its dedicated tracing hotline for help.

Police asked that residents refrain from sharing unconfirmed news, or images of the ongoing security operation on social media, cautioning about misinformation circulating online.

Before the evacuation, an explosion and gunfire from inside the hotel was heard by an eyewitness near the complex.

The latest attack began at a bank inside the compound Tuesday afternoon. An explosion ripped through three vehicles in the parking lot, followed by a suicide blast in the foyer of the Dusit Hotel, said Boinnet, the nation’s police chief.

Attack started with car bombs

Heavy gunfire and an explosion sent people running for their lives. Footage from the scene showed armed officers escorting office workers and injured people to safety as the sound of shots rang out. Cars in the compound could be seen aflame as a helicopter flew overhead.

Security forces responding to the scene.

Kenyan anti-terror units, other law enforcement agencies and ambulances rushed to the scene on Riverside Drive in Nairobi’s Westlands affluent neighborhood as people with bloodied clothes could be seen fleeing the complex. Nearby, students from the University of Nairobi’s Chiromo campus were evacuated onto the street.

“As we were leaving, there were gunshots all over the place,” said Evans Ng’ong’a, who was also inside the complex. “Attackers jumped over the fence and started shooting after the explosion.”

Ng’ong’a shared videos and photos on Twitter of an ongoing police operation.

International response

US Ambassador to Kenya Bob Godec condemned the attacks in a series of tweets and offered US assistance. He confirmed that all embassy personnel are safe.

UN Secretary-General António Guterres also condemned the attack and expressed “his solidarity with the people and government of Kenya,” according to a statement. The UK High Commissioner to Kenya, Nic Hailey, tweeted that his team “will be working through the night to support the Kenyan authorities as they respond to this horrific attack and support any Brits who need our help.”

People run for cover after being rescued from the compound.

The attack drew immediate comparisons to the 2013 Westgate mall attack in Nairobi when Al-Shabaab extremists killed 67 people at the luxury shopping center.

Tuesday marks the three-year anniversary of an Al-Shabaab attack on the El Adde military base, which left more than 140 Kenyan soldiers dead.

CNN’s Richard Roth, Jennifer Hansler, Sam Kiley, AnneClaire Stapleton and Gianluca Mezzofiore contributed to this report.