Medical workers in Yemen say security forces have fired on anti-government protesters in the capital, Sana'a, killing at least two people.
Medics say the troops loyal to President Ali Abdullah Saleh also wounded at least 40 people Tuesday as tens of thousands of protesters continued their call for the president to step down.
There are reports that government troops later clashed with dissident soldiers in the capital.
Saleh said Monday he welcomed a U.N. Security Council resolution urging him to leave office and that he is ready for talks to put a deal in motion.
A Gulf Cooperation Council proposal offers Saleh immunity from prosecution if he hands power to a deputy within 30 days. On at least three occasions, Saleh has refused to sign the plan, saying he first wants international guarantees about a timetable for its implementation.
Also Tuesday, Yemeni security officials say a military plane crashed while landing at an air base in the country's south, killing at least four people.
Officials said the crash in Lahej province was likely caused by a technical problem.
Reports say there were 15 people on board the plane, eight Syrians and seven Yemenis.
Yemeni troops have been battling al-Qaida-linked militants in the south for months as political unrest also grips the country.
Some information for this report was provided by AP, AFP and Reuters.