Security forces loyal to embattled Yemeni President Ali Abdullah Saleh fired tear gas and live ammunition at anti-government demonstrators in the capital, Sana'a Saturday, killing at least 18 people and wounding dozens of others.

Activists and witnesses said at least 12 of the deaths occurred when security forces opened fire on protesters in the city center, while the rest was killed elsewhere in the capital as security forces battled supporters of opposition tribal leaders and dissenting soldiers.

The opposition march began at Sana'a University, where demonstrators shouted anti-government slogans and carried banners calling for President Saleh's resignation.

Deputy Information Minister Abdou Janadi said the casualties were “unfortunate.” He accused the opposition of provoking the clashes and using the protesters as human shield.

The anti-government unrest has come at a time when the embattled leader is also dealing with militant-related unrest in some regions of Yemen.

In other violence, nine al-Qaida militants were killed in suspected U.S. airstrikes targeting al-Qaida positions in southeastern Shabwa province overnight.

Local officials said the dead militants included the media chief for al-Qaida Yemen branch, Egyptian-born Ibrahim al-Bana, and a son of slain U.S. born cleric Anwar al-Awlaki with ties to the terror group.

Hours after the airstrikes, suspected militants blew up a gas pipeline in what may have been a retaliatory act. Officials said operations were halted at a gas supply terminal as a result.