Unidentified gunmen killed four people and injured several others in the conflict-ridden Kenyan port city of Mombasa, BBC reported Monday.

Robert Kitur, the police chief in Mombasa, told Associated Press that three gunmen opened fire indiscriminately in the city's Soweto slum Sunday night. "They did not steal anything. They just shot," he added. Kitur said the police were trying to identify the gunmen.

Peter Muskoyi, a Mombasa resident, told reporters that the attack was carried out by men “dressed in black with a red ribbon around their heads.” He also said that they scattered leaflets stating that Sunday's attack was retribution for the killings in June in Mpeketoni, a town about 180 miles north of Mombasa.

More than 60 people, most of them ethnic Kikuyus, were killed and several buildings were burned down in the attacks in Mpeketoni for which Somalia-based militant group al-Shabaab claimed responsibility. In a statement sent to Al Jazeera, the group had stated at the time that "the Mpeketoni raid was carried out in response to Kenyan military's continued invasion and occupation of our Muslim lands and the massacre of innocent Muslims in Somalia.”

Sunday’s attacks are the latest in a series of ethnic and religious clashes the country has witnessed in the last few months.

More than 90 people have died in Mombasa -- Kenya’s second-largest city -- in less than a month in a number of bombings and gun attacks. While the violence has largely been attributed to al-Shabaab, many, including President Uhuru Kenyatta -- a Kikuyu himself -- have suggested that local politicians were behind the attacks.

Kenya has been in the grip of sporadic ethnic clashes since the disputed presidential elections of 2007, when Mwai Kibaki, from the Kikuyu community, was re-elected. This led to clashes between Kikuyus, Kalenjins and Luos, which have led to the deaths of over 2,000 people and crippled the country’s economy.

Following months of violence, several countries, including the U.S. and the U.K., have issued warnings advising their citizens against travelling to Mombasa.

No group has yet claimed responsibility for Sunday’s attacks.