A blast, possibly caused by a car bomb, went off near the international airport in the Somali capital on Wednesday where the United Nations and some Western embassies are based, a Reuters witness and a security official said.
There was no word on casualties and no immediate claim of responsibility. The Somali Islamist group al Shabaab has often used car bombs.
A security adviser, based at the airport, told Reuters by telephone there had been a suspected VBIED, or vehicle-borne improvised explosive device, without giving further details. Another official said the blast was just outside the airport.
The airport has a tight security cordon and blast walls, and is used as a base for U.N. operations in Somalia. The airport area is also the home to the British and Italian embassies.
The al Qaeda-linked group, which wants to impose its strict interpretation of Islamic law on Somalia, has launched a string of bomb and gun attacks in Mogadishu and other centres.
The group promised to step up attacks after African Union and Somali troops launched an offensive this year that has driven the group from major strongholds, including its last major coastal base of Barawe in October.