A suspected Al-Shabaab militant has been shot dead after he stabbed a Kenyan police officer guarding the US embassy in Nairobi.

The man, it is reported, was trying to forcefully gain entry into the embassy when he was blocked by the officer at the gate.

"The man was shot after stabbing a GSU officer in the hand and left him with injuries," Gigiri police boss Vitalis Otieno told Nation.

Mr Otieno said the dead man had been walking towards the US embassy and was close to the public entrance to the visa section when he attempted to grab a gun from one of the officers.

A photograph shared on social media showed the body of a man of apparently Somali origin lying on the pavement, a pool of blood staining the tarmac by his head, and surrounded by police officers. US Federal Bureau of Investigation (FBI) officers were also present at the scene.

A statement from the US embassy confirmed the "shooting incident", adding that "no embassy personnel were involved. We refer you to Kenyan authorities for further details."

The well-guarded US embassy in Nairobi is located opposite the main UN complex in Gigiri, an upmarket suburb in the city's north popular with expatriates.