(updates death toll in lede, head))

Witnesses and medics say Yemeni security forces killed at least 15 people Sunday when they fired on anti-government protesters in the capital, Sana'a.

Witnesses say the attack by security forces wounded dozens of other protesters at one of the largest demonstrations in months against President Ali Abdullah Saleh.

The recent clashes between security forces and opposition protesters in the capital started late Friday into early Saturday, when witnesses said security forces fired at anti-government protesters who were camped out in a square.

The demonstrators are demanding that Mr. Saleh step down.

The president remains in Saudi Arabia, where he has been recovering from injuries sustained in a June attack on his presidential compound. Earlier this month, he authorized a deputy to talk with the opposition in an effort to put an end to the crisis that has gone on for months.

In April, the six-nation Gulf Cooperation Council proposed a plan designed to end Yemen's anti-government turmoil. Mr. Saleh agreed to the proposal three times, but each time backed out before the deal could be signed.