Renewed clashes between troops loyal to Yemeni President Ali Abdullah Saleh and opposition tribesmen have killed at least two people in a northern district of the capital, Sana'a, as violence continued in the country's volatile south.

Residents said artillery and automatic weapons fire was concentrated early Thursday near the home of a prominent anti-Saleh tribal leader in Sana'a's Hasaba district, the site of weeks of bloody fighting that began in May.

On Wednesday, Yemeni forces killed at least 12 militants in southern Abyan province, just days after the government said it had “liberated” the provincial capital of Zinjibar from Islamist fighters.

In the southern coastal city of Aden, at least two explosions hit the intelligence headquarters and a police base, causing little damage. A young boy was shot dead when security forces responded with heavy gunfire.

Army officials said negotiations with southern militants to end the bloodshed there are deadlocked. The Yemeni government has been fighting to retake control of Zinjibar and other parts of Abyan from al-Qaida-linked fighters who seized the area in May.

Opposition protesters and tribesmen have been demonstrating since February for an immediate end to Mr. Saleh's 33-year autocratic rule. Yemeni troops and Saleh loyalists have cracked down on protesters and tribesmen who have taken up arms against the government.

On Tuesday, the U.N. High Commissioner for Human Rights said hundreds of people have been killed in six-months of protest-related violence. The commissioner's office also accused the Yemeni government of using excessive lethal force against peaceful activists protesting for greater freedoms.

Mr. Saleh, recovering in Saudi Arabia from an assassination attempt in June, continues to maintain power despite international pressure to quit and the ongoing street protests.