One demonstrator was killed and 11 injured on Saturday in a southern town when police descended on thousands rallying for the ouster of Yemen's longtime president, an activist said.

Nouh al-Wafi said police fired tear gas and live ammunition to disperse protesters in the town of al-Maafir in Taiz province. The demonstrators were mainly students but were joined later by other residents.

In several other cities — including Aden, Saada and Hodeida — protesters observed a one-day shutdown of offices and businesses Saturday as part of the civil disobedience campaign called by the opposition to pressure President Ali Abdullah Saleh to step down.

Thousands of people also demonstrated in the southern cities of Ibb and Hadramawt, the latest in daily protests that have been staged for almost three months. The youth movement leading the protests issued a statement insisting Saleh resign immediately, opposing any attempts to amend the Gulf Cooperation Council proposals for him to relinquish power more gradually.

The mediation plan looked close to success a week ago, with both the opposition political parties and Saleh agreeing to it, until the president balked just days before the signing ceremony. The plan called for Saleh to step down within 30 days, with a promise of immunity from prosecution, and for a national unity government to run the country until elections are held.

The leaders of the street protests did not participate in the talks and rejected anything short of Saleh's immediate ouster and his trial over corruption and the killings of protesters. They say the country's established opposition political parties, which have taken part in the talks, do not represent them.

However, Mohammed al-Sabri, a spokesman for the opposition parties, said Saturday that they reject any changes in the proposals to accommodate Saleh.

"We have informed the Gulf people that the issue has been dragging for a long time with Saleh's unacceptable and meaningless evasiveness," he said. "The people are fed up with the current situation and don't accept more procrastination."

He accused the United States and the Europeans of trying to add new ideas to the proposals in favor of Saleh, who has been in power for 32 years.

Al-Sabri said the opposition would wait for Saleh until Tuesday "to announce once and for all either he accepts or rejects the proposals, otherwise, the people have their own alternatives." He did not elaborate.

The official Sabaa news agency said Saleh met Saturday with the United Nations secretary general's envoy, Gamal bin Omar, to discuss the latest developments.

Sabaa quoted bin Omar as saying that the United Nations was eager to help Yemen to overcome its current crisis. The envoy met later with the leaders of the opposition parties.

At least 140 people have been killed in the government's crackdown on the protesters — prompting several top military commanders, ruling party members and diplomats to defect to the opposition.

The country has been wracked in recent years by widespread corruption, a weak central government, a Shiite rebellion in the north, a secessionist movement in the south and one of the most active branches of al-Qaida operating in the remote hinterlands.