Yemeni government forces and allied tribesmen killed ten militants in attacks around the country Sunday, security officials said, as a visiting United Nations envoy met with embattled President Ali Abdullah Saleh to push for a solution to the country's political crisis. Security has collapsed across the Arab world's poorest nation during the nine-month popular uprising seeking to oust Saleh, who has been in power for 30 years. Pro-Saleh forces regularly engage in deadly clashes with armed tribesmen and military defectors who support the protesters in Yemen's largest cities, and al-Qaida-linked militants have overrun entire towns in the country's restive south. Meanwhile, international diplomacy has failed to stop the crisis. Saleh has refused numerous times to follow through with a U.S.-backed proposal crafted by Yemen's powerful Gulf Arab neighbors under which he would transfer power to his vice president in exchange for immunity from prosecution. Two of Sunday's clashes took place near Zinjibar, the largest town overrun by al-Qaida-linked militants in Yemen's southern Abyan province, now partially recaptured by the army. In one clash, tribesmen allied with government forces exchanged fire with militants at a checkpoint, killing three including two Somali citizens, an official said. In the other, the army shelled a militant position, killing five including two Saudi citizens.