Massive rallies are unfolding across Yemen on Friday as anti-government activists renew calls for change.

Demonstrators are seeking an end to President Ali Abdullah Saleh's 33-year rule.

Mr. Saleh remains in Saudi Arabia where he is recovering from injuries sustained in a June attack on his presidential compound.

On Thursday, heavy clashes between Yemeni forces and armed tribesmen who attacked a Republican Guard training facility killed dozens of people 40 kilometers north of the capital, Sana'a.

Yemeni officials said the elite unit, backed by government warplanes, shelled and bombed hundreds of tribesmen who had seized part of the al-Samaa military camp.

The Defense Ministry said loyalist troops suffered “heavy losses” and the attackers sought to gain control of Sana'a International Airport. Tribal sources confirmed casualties, saying “dozens were killed and wounded” from both sides.

The government accused the Islamist opposition Al-Islah party militia of involvement in the raid on the training camp.

Separately, at least one soldier was killed and another wounded in the southern city of Taiz near a square where anti-government protesters have been camped for months.