At least 10,000 people have fled fresh violence in Somalia's capital Mogadishu in the past week, the UN says.
Soldiers are on high alert outside the peace talks
A report by the UN refugee agency says violence has surged since the launch of national reconciliation talks recently and has prompted the fresh exodus.
On Sunday, four civilians were killed following a series of explosions at Mogadishu's main Bakara market.
Mogadishu has seen a series of blasts targeting interim government officials since Islamists were ousted last year.
Somalia has been without a functioning government for the past 16 years.
The BBC's Mohammed Olad Hassan in Mogadishu says the civilians were killed after government soldiers opened fire indiscriminately when grenades were aimed at their convoy.
President Yusuf said a nuclear bomb would not stop the talks
Government troops have been searching for weapons at the main Bakara market for the past 18 days and are facing great resistance.
"No soldier was killed and they did not target civilians following the explosions. They only fired in self defence," said army commander Col Farah Abdulle.
Figures compiled by the UNHCR indicate that nearly 21,000 people have fled Mogadishu between June and July and the pace is rising.
Some 125,000 out of the estimated 400,000 people who fled the capital during clashes between Ethiopian-backed government troops and Hawiye clan fighters between February and May, have returned to Mogadishu, the report says.
The UN refugee agency says attacks launched by anti-government elements wound and kill civilians daily and the prospect of still another round of heavy fighting has driven people onto the road once more.