Somali security forces arrested a former minister and presidential candidate in an overnight raid on his home in which they killed five of his bodyguards, police and lawmakers said on Monday.

A spokesman for the Internal Security Ministry said Abdirahman Abdishakur was accused of treason. Abdishakur, who stood in the February presidential election, is an opposition politician and an outspoken critic of the weak, United Nations-backed government led by President Mohamed Abdullahi Mohamed.

"The former minister was legally arrested by decree from the attorney general and internal security minister. He was accused of treason. His guards fought the security forces," spokesman Abdiasis Ali told reporters on Monday.

A policeman confirmed five bodyguards were killed in the raid, while a local elder Abdullahi Ali told Reuters Abdishakur had been injured on the arm by a stray bullet.

The raid drew angry responses from lawmakers and protesters. Hundreds of people marched in Mogadishu on Monday as government forces deployed to block main roads.

"What the government is doing is against Islam and healthy politics," lawmaker Mahad Salad told Reuters. "We condemn the government's immoral act. We also order for the release of the ex-minister."

The presidential election in February was praised by Western donors as a modest step forward from the previous election and it raised hopes that the country might be able to more effectively combat Islamist insurgents.

But the insurgency is striking with ever larger and more deadly attacks in the capital and major towns.

Reuters reported last week that the United States is suspending food and fuel aid for most of Somalia's armed forces over corruption concerns, a blow to the military as African peacekeepers start to withdraw this month.