A grenade thrown at protesters rallying in the Yemeni city of Taiz killed one person and wounded 28 others on Friday, hospital sources said.
A car drove up to the 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, witnesses said.
"The car got close to the square and someone threw a bomb that exploded in the middle of the crowd, it was terrifying," said one protester, who asked not to be named.
Several ambulances rushed to Hurriya (Freedom) Square, where the Taiz protesters have camped out for days.
A senior interior ministry official told Reuters police had found the car and arrested its driver.
"They got the car and caught the man suspected of throwing the grenade and they are questioning him," the official said.
Protesters said the government 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, told Reuters.
At least 10,000 protesters were gathered in Hurriya Square, and similar numbers of Saleh loyalists were rallying in downtown Taiz, around 200 km (120 miles) south of Sanaa.
Saleh is struggling to end month-old protests across the impoverished country that are now erupting on a daily basis.
In a sop to protesters, Saleh has promised to step down when his term ends in 2013 and not hand power to his son.
A coalition of opposition parties, which had laid on rallies that drew tens of thousands, has now agreed to talk to him, but smaller, more spontaneous protests have continued, organised by students and others using mobile text messages and Facebook.
AgenciesLast Mod: 18 Şubat 2011, 17:58