SANAA (Reuters) - Yemeni President Ali Abdullah Saleh was slightly wounded when shells struck his palace in Sanaa on Friday, an official said, as fighting intensified that pushed the impoverished country closer toward civil war.
Fierce fighting engulfed the Yemeni capital, where residents cowered in their homes as explosions rocked the city, and questions arose over Saleh's health after he failed to appear at a planned news conference after the sprawling palace was hit.
Yemen's deputy information minister said the 69-year-old president had postponed his appearance because he was being treated for "scratches".
"The president is in good health and has postponed the press conference... due to scratches," Abdu al-Janadi told journalists. "There is nothing that affects his health."
A senior diplomat in Sanaa said the prime minister, his deputy, the parliament speaker and other aides were hurt and a source inside Saleh's office confirmed that government officials had been wounded in the attack. He had no details.
The state news agency Saba said three presidential guards were killed at a mosque inside the palace compound.
"A cowardly attack with an explosive projectile took place during Friday prayers at the presidential palace mosque where ... Saleh and senior government officials were present.
The government blamed the shelling on Hashed tribesmen led by Sadeq al-Ahmar, whose family has backed protesters demanding Saleh's overthrow. Ahmar later denied responsibility and accused Saleh himself of orchestrating the attack to justify a government escalation of street fighting in the capital.
Suspicion also has fallen on breakaway General Ali Mohsen, who defected to the opposition in April and sent his troops to the capital to protect anti-Saleh demonstrators.
Forces loyal to Saleh later shelled the homes of the leaders of the Hashed tribal federation, security sources said.
The United States condemned the escalating violence and called for an orderly and peaceful transfer of power.
"Violence cannot resolve the issues that confront Yemen, and today's events cannot be a justification for a new round of fighting," White House press secretary Jay Carney said in a statement.
Saleh has exasperated his former U.S. and Saudi allies who had once seen him as a key partner in efforts to combat al Qaeda's ambitious Yemen-based wing, known as al Qaeda in the Arabian Peninsula (AQAP).
Yemen has tipped swiftly towards civil war this week, with Hashed tribesmen battling Saleh forces in Sanaa.
More than 370 people have been killed, at least 155 of them in the last 10 days, since a popular uprising began in January against Saleh's nearly 33 years in power.
Defying world pressure, Saleh has thrice reneged on a deal brokered by Gulf states for him to quit in return for immunity from prosecution, even as he haemorrhages support at home.
The secretary-general of the Saudi-led Gulf Cooperation Council (GCC) urged all parties in Yemen to end the fighting.
"The ministerial council of the GCC is following with concern and sadness the deteriorating situation and the continued fighting. This situation is regrettable and benefits no one," Abdulattif al-Zayani told Al Arabiya television.
Yemen's increasingly bloody struggle looks sure to go on as long as Saleh refuses to step down and it will complicate the already formidable challenge of uniting the country and rebuilding shattered state institutions in any post-Saleh era.
Instability in Yemen could threaten regional security and possibly global oil supplies due to its proximity to the world's largest oil exporter, Saudi Arabia, and vital shipping lanes.
"The dangers a collapsed Yemen poses for the region are too horrendous to contemplate," said Ghanem Nuseibeh, founder of Cornerstone Global Associates and senior analyst at Political Capital. "Although the border with Saudi Arabia is more secure than in recent years, it is still a relatively porous border.
"The consequences will be on the security front, as well as economic. AQAP in particular will find comfort in a failed Yemen, and threaten the rest of the GCC and (this) will have implications for piracy across the Gulf of Aden," he said.
Before the attack on the palace, protesters paraded the coffins of 50 people it said were killed by Saleh's forces since a ceasefire fell apart this week.
Heavy fighting spread for the first time to southern Sanaa, held by Saleh loyalists battling disaffected military units and tribesmen in the north. Thousands of civilians have fled.
Explosions were also heard in the southern city of Taiz, where the United Nations has said it is investigating reports that 50 people have been killed since Sunday.
Three policemen were killed by a rocket-propelled grenade attack in Taiz and 28 were wounded in clashes with protesters, sources at military hospital said. Two protesters were killed and 30 wounded, sources at the city's al-Thawra hospital said.
The bloodshed has eclipsed a mostly peaceful pro-democracy movement inspired by successful revolts in Egypt and Tunisia.
Yemen is engulfed in multiple conflicts, with street battles between tribal groups and Saleh's forces in Sanaa, popular unrest across the country and fighting against AQAP and other Islamist militants who seized the coastal city of Zinjibar.
Four civilians and five militants were killed by air strikes on Zinjibar on Friday, according to a government official.
One constant factor is Yemen's crippling poverty. Jobs and food are scarce, corruption is rampant and two-fifths of the 23 million people struggle to live on less than $2 a day.
"Economic migrants will also pose a challenge for the region. We are getting very close to an irreversible situation," Nuseibeh said. Tribes might start fighting among themselves, especially those close to the Saudis and those which are not.
"The danger is that this civil war is not along north-south lines but more internalised, within regions. When the conflict turns tribal, as well as nationalistic along the former north-south borders, it becomes very difficult to stop."
(Additional reporting by Mohammed al-Ramahi in Sanaa, Mohammed Mukhashaf in Aden, Khaled al-Mahdi in Taiz, Mahmoud Habboush and Jon Herskovitz in Dubai and Samia Nakhoul in London; Writing by Alistair Lyon; Editing by Michael Roddy)