Somali police said they have foiled a planned terrorist attack on Mogadishu on the eve of Ramadan on Sunday.

One police officer was killed when a device found in a minibus exploded as a team tried to defuse it, deputy police commander Zakia Hussein Ahmed said.

The explosion, which occurred about 15 kilometers south of Mogadishu, was heard in the capital.

"The terrorists were planning to bring the explosive-laden car into Mogadishu to harm civilians during Ramadan," Ahmed said.

Police did not say who was responsible or whether any arrests had been made.

Separately, police said explosive devices belonging to terrorist group al-Shabaab were found and confiscated in the coastal city of Marka in the Lower Shabelle region earlier Sunday.

Security has been beefed up around Mogadishu for the start of the Muslim holy month.