Fierce street battles flared up early Thursday in Yemen's capital between government forces and opposition armed rebels, leaving at least two rebels killed and three others injured, a security official and an opposition online website said.

An official of the Interior Ministry told Xinhua on condition of anonymity that "mortar shells and heavy shoot-out rang out near the headquarters of the Interior Ministry in volatile Hassaba district in downtown Sanaa."

"The opposition is seeking to spark a civil war through its aggression against security forces today," the security official added.

However, the opposition al-Masdar online website said "At least two armed tribesmen of the opposition tribal leader Sadiq al-Ahmar were killed and three other fighters were wounded when security forces loyal to President Ali Abdullah Saleh opened heavy fire on the opposition residential compound of al-Ahmar in Hassaba district near the headquarters of the Interior Ministry."

Meanwhile, many residents said that they heard "huge explosions and heavy shooting near the 60th Street," which located between the defected army's military base and the residential compound of Vice President Abd-Rabbu Mansour Hadi in the western part of the capital."

Huge explosions have rocked Sanaa for about two hours at night as the shelling is still continuing.

Thursday's heavy gunfire came as the second of its kind as Hassaba district witnessed weeks-long fierce street battles between al-Ahmar's militants and the government troops late in May after President Saleh refused to sign a power-transition deal initiated by the Gulf Cooperation Council (GCC) for the third time.

Al-Ahmar, the chieftain of the powerful Hashid Tribes Confederation, who is also appointed as the leader of anti- Saleh tribal alliance, pledged last month in a press conference to "work to prevent Saleh from ruling the country again as long as he is alive."

Saleh, who confronted eight-month of protests demanding an end to his 33-year rule, is still in Saudi Arabia for rehabilitation from wounds he sustained in a shelling attack on his compound in Sanaa on June 3.

Earlier this week, the embattled president issued a decree authorizing his deputy Hadi to sign the GCC initiative after launching a dialogue with the opposition to set a timetable and a mechanism to transfer power.

The opposition, however, rejected Saleh's move and required him to sign the deal first rather than resorting to "unacceptable and complicated" political maneuver.