Eight anti-government protesters in the Yemeni city of Taiz were wounded when an assailant threw a hand grenade at them, opposition sources and witnesses said.

A car drove up to protesters, who are demanding an end to President Ali Abdullah Saleh's three decade rule, and one of the passengers threw a grenade out the window, a witness said.

"The car got close to the square and someone threw a bomb that exploded in the middle of the protesters, it was terrifying," he said, declining to be named.

Several ambulances rushed to Hurriya (Freedom) Square, where the Taiz protesters have camped out for days.

Protesters blamed the government, saying it was behind the attack, but said they would not retreat from the square.

"It's just shameful that the government would resort to these criminal tactics. But it won't scare off the protesters," a protester, who declined to be named, said.

At least 10,000 protesters were gathered in Hurriya Square, and similar numbers of Saleh loyalists were rallying in downtown Taiz, around 200 km south of Sanaa, Reuters reports.