Yemeni President Ali Abdullah Saleh has yet to appear in public after being wounded by rockets fired into the presidential compound in the capital, Sana'a.

Yemen state media had said the president would address the nation Friday, just hours after the attack – evidently to refute a report aired by an opposition-controlled television station that he was killed during the shelling.

As hours passed, there was no sign of Mr. Saleh, however. State television said only that he was “well” following the attack. One pan-Arab television network Mr. Saleh was receiving medical treatment at a military hospital.

Western media accounts quote an opposition report that Mr. Saleh was attending prayers at a mosque in the presidential compound at the time of the rocket attack. No group claimed responsibility.

Yemen's state news agency said three guards were killed and the imam leading the prayers was wounded. Other reports said several other high-ranking officials, including Prime Minister Ali Mohammed Mujawar, were also at the mosque.

The United States strongly condemned the upsurge in violence in Yemen on Friday.

A State Department statement called for an immediate end to hostilities and fulfillment of an Arab Gulf peace plan that calls for Mr. Saleh's departure.

Residents in the capital remained barricaded behind closed doors as fighting raged in Sana'a after dusk.

Earlier Friday, clashes between President Saleh's forces and loyalists to an opposition tribal leader, Sheik Sadeq al-Ahmar, escalated with the destruction of the headquarters of an opposition TV station in Sana'a.

Reports said fighting in the capital had expanded into new neighborhoods, and opposition tribesmen were traveling to Sana'a to take part in the fighting. Government forces reportedly shelled al-Ahmar's tribal headquarters after the mosque attack.

The rising chaos is pushing the conflict closer to all-out civil war. Government troops are said to have killed 50 opposition members in fighting this week.

Yemen is engulfed by multiple conflicts, with street battles raging in Sana'a, popular unrest by anti-government demonstrators throughout the country and fighting against Islamist militants who have seized the southern city of Zinjibar.

In the southern city of Taiz, government forces and protesters clashed Thursday. At least 25 people have died in the violence in Taiz in the past few days.

U.S. envoy John Brennan, President Obama's top counterterrorism adviser, left the U.S. Thursday to travel to the United Arab Emirates to continue talks on Yemen. He is seeking help to pressure President Saleh to accept a deal brokered by regional powers that would secure a peaceful end to his nearly 33-year rule.

The fighting in Sana'a broke out last week when pro-Saleh forces moved against al-Ahmar's compound in Hasaba, a district of the capital. In March, the al-Ahmar family had announced that the Hashid confederation – the country's most powerful tribal alliance – would back the protest movement, but its armed fighters had avoided clashes with Mr. Saleh's forces.