By Abdi Sheikh and Feisal Omar
MOGADISHU, April 22 (Reuters) - Islamist rebels shot dead a Somali lawmaker on Tuesday, a day after blowing up one of his colleagues, and vowed to keep killing politicians and wreck efforts to secure the country.
Al Qaeda-linked group al Shabaab told Reuters they wanted to send a message to Western-backed President Hassan Sheikh Mohamud, who on Tuesday was due to wrap up a three-day conference on improving security in the capital.
"This proves that they cannot and will never do anything about security ... More serious killings are on the way," said al Shabaab's military spokesman, Sheikh Abdiasis Abu Musab.
Somalia's two decades of civil war and lawlessness, triggered by the overthrow of President Siad Barre in 1991, has already spread to destablise the region.
Western nations fear Somalia could sink further into chaos and provide a major launchpad for Islamist militancy.
Dahir Amin Jesow said fellow member of parliament Abdiasis Mursal was killed outside his house in Mogadishu's Madina district.
"Men with pistols hit him with several bullets in the chest and in the head. He died on the spot," Jesow said.
Somali Prime Minister Abdiweli Sheikh Ahmed said the violence would not deter his government from securing peace.
"The use of terror ... only serves to unite and strengthen our resolve," he added.
Al Shabaab had said Monday's killing of a lawmaker with a car bomb was meant to punish politicians who backed the "invasion of the Christians into Somalia", a reference to the support Mogadishu receives from Western governments and African Union members who have sent in troops to battle the rebels.
Al Shabaab was pushed out of the capital in 2011 but has since waged a bombing campaign in a bid to overthrow the government and impose its strict version of Islamic law.
It claimed responsibility for last year's attack on the Westgate shopping mall in Kenya's capital Nairobi in which at least 67 people died. (Writing by Drazen Jorgic; Editing by Andrew Heavens)