A group of armed men attacked an upscale shopping mall in Nairobi on Saturday, killing at least five people and wounding dozens. There were reports of gunshots and explosions but no clear motive as the situation unfolded.

By midafternoon, police officers were swarming the mall and the gunmen were still inside.

The police said that four people had been wounded but had not yet confirmed any fatalities.

The police said they had surrounded the mall. While they urged the public to remain calm and avoid speculation, for years there have been growing concerns that the Somali militant group Shabab would try to pull off another significant attack in the Kenyan capital.

But Nairobi’s police chief, Benson Kibue, said that the attack was the result of an attempted robbery.

Witnesses described attackers using AK-47s and throwing grenades.

On weekends the mall is heavily trafficked by shoppers, including both well-to-do Kenyans and members of the city’s large expatriate community.