Somalias Prime Minister Omar Abdirashid Ali Sharmarke resigned Tuesday after a month of disagreements with President Sheikh Sharif Ahmed. President Ahmed's UN-backed government is battling Islamist group al-Shabab for control of the capital, Mogadishu. Sources said that his squabbling with the prime minister has hampered the fight against the insurgents. Omar Abdirashid Ali Sharmarke has been under intense pressure to resign for some months. He said he had been unable to work with the president.Sharmarke and Sharif have clashed over a number of issues including a new constitution for Somalia. The resignation comes as violence continued in Mogadishu.In the latest incident, a lone gunman tried to force his way into the presidential palace Monday night, according to the director of communication of the president, Abdirashid Khalif.The gunman, who had a grenade and a rifle, was shot dead by security guards, Khalif said.