The National Intelligence and Security Agency (Nisa) said in a tweet that it had briefed the nation’s leaders on the "plot being hatched by the al-Shabab mafia".

The agency did not provide further details, but said that it was pursuing everyone involved.

The warning comes amid a political crisis in the country due to the much-delayed indirect elections.

Al-Shabab has also intensified attacks across Somalia.

The group recently attacked a heavily-fortified airport complex which houses UN offices, foreign embassies and various diplomatic missions in the Somali capital, Mogadishu.

It also carried out two suicide bombings in the central Beledweyne town, killing at least 48 people, including a female member of the federal parliament.