SANAA, Yemen - Yemeni security forces clashed with thousands of protesters who hurled rocks and burned tires in the southern port city of Aden on Wednesday, killing at least one person as demonstrations swelled in the capital.

Yemen has been wracked by protests since mid-February demanding President Ali Abdullah Saleh resign because of the country's lack of freedoms and extreme poverty. More than 120 people have been killed since the uprising began on Feb. 11, inspired by popular uprisings in Tunisia and Egypt.

The army and anti-riot police, backed with tanks and artillery, fired live ammunition and tear gas in Aden, according to eyewitnesses. Medical officials said one person was killed and seven wounded.

The witnesses and officials spoke on condition of anonymity because they were not authorized to speak to the media.

In the capital Sanaa, armed civilians attacked an army unit affiliated to Maj. Gen. Ali Mohsen al-Ahmar, who had earlier defected to the opposition. One officer was killed and two were wounded, according to military officer close to al-Ahmar.

Also in the capital, tens of thousands of anti-government protesters took to the streets.

Saleh has offered to step down at the end of this year if an acceptable transfer of power is reached, but the opposition fears he is just stalling for time.

The six-nation Gulf Cooperation Council offered its own proposal Sunday to end the unrest and called on Saleh to transfer power to his deputy as part of a deal with the opposition. The deal did not, however, specify a timeframe and included immunity from prosecution for Saleh and his family.

The opposition Civil Alliance of the Youth Revolution, which includes 30 youth groups, rejected the proposal.

"The initiative does not clearly mention the immediate departure of the head of the regime and it did not touch on the fate of his relatives who are at the top military and security agencies that continue killing the peaceful protesters," the alliance said in a statement.

In response, the president's office issued a statement Tuesday saying Saleh "has repeatedly expressed no reservations to the peaceful and smooth transfer of power within the constitution," which would allow him to remain in office until the 2013 elections -- an option long rejected by protesters