The incident took place at the frontier between the Somali town Bulo Hawo and Kenya's Mandera, close to where the border meets Ethiopia to the north.

Multiple sources told AFP the exchange was triggered when a group of Somali demonstrators angry at the alleged killing of three civilians approached border posts manned by Kenyan soldiers.

"Kenyan troops opened fire on Somali protesters who closed (in) on their positions along the Bulo Hawo boarder and the Somali troops stationed close to the area responded with heavy fire, this continued for several minutes," Bulo Hawo police officer Mohamed Abdirahman told AFP by phone.

None of the sources contacted by AFP reported any casualties from the brief exchange of fire.

The demonstrators believed that three civilians "kidnapped the day before" in the border town of El Wak, south of Bulo Hawo, had been killed by Kenyan anti-terror police, Abdirahman said.

They "were dispersed with heavy gunfire by the Kenyan troops," eyewitness Abdifatah Hassan said. "The Somali forces close to the area intervened in the situation by engaging (in a) gunfight with the Kenyans."

A Kenyan security official confirmed to AFP that "there was gunfire at the border where SNA (Somali National Army) and KDF (Kenya Defence Forces) exchanged gunfire after some incident of protests".

"The locals on the other side are accusing Kenyan forces of killing three civilians who were not Al-Shabaab," he added, referring to the Al-Qaeda-affiliated Islamist militant group active in Somalia.

The Somali government has so far not acknowledged the incident.

Striking from Somali territory, Al-Shabaab regularly defies Kenyan army troops to attack towns along the two countries' long shared border.

Over the past year, relations between Nairobi and Mogadishu have soured, especially over a political crisis in the semi-autonomous Jubaland region of Somalia.

The Somali government has refused to acknowledge the contested reelection in August 2019 of Jubaland president Ahmed Madobe, a political ally of Kenya's.

Somalia accuses its larger neighbour of interference in its internal affairs, in particular through its support for Madobe.

Tensions were stoked in March when fierce fighting broke out between Somali and Jubaland troops, also near Mandera.