Prince Bandar bin Sultan, the former Saudi ambassador to the United States, has been named the country's new intelligence chief, the royal palace announced on Thursday.

Prince Bandar, who retains his job as secretary general of Saudi Arabia's National Security Council, replaces Mogren bin Abdel Aziz, who resigned.

Ramadan will begin on Friday in most Arab countries, religious authorities announced, but in Oman and Syria as well as for Iraq's Sunni Muslims and in non-Arab Iran it will start on Saturday.

Egypt, Jordan, Kuwait, Qatar, Saudi Arabia, Tunisia, the United Arab Emirates and Yemen, as well as Lebanon's Sunni Muslims, were among those to announce a Friday start.

The killing of three top regime officials has dealt President Bashar Assad a severe blow, but he has no intention to give up his power, experts said on Thursday.

Both the regime and the rebels believe they are winning as clashes engulf Damascus, for the fifth consecutive day, and a day after an attack struck the National Security headquarters, killing Assad's brother-in-law Assef Shawkat, defense minister Daoud Rajha and crisis cell chief Hassan Turkmani.

The Syrian regime is in its last days, the head of the main exiled opposition group said on Thursday, warning that a veto by Russia and China at the United Nations could have "disastrous" consequences.

"The regime is in its final days," Syrian National Council chief Abdel Basset Sayda said following talks in Rome with Italian Foreign Minister Giulio Terzi shortly after the veto at the U.N. Security Council in New York.

Syrian rebels took control of all border crossings between Iraq and Syria on Thursday, Baghdad's deputy interior minister told Agence France Presse, as a rights group said rebels also seized a crossing on the border with Turkey.

"All the border points between Iraq and Syria are under the control of the Free Syrian Army," Adnan al-Assadi told AFP by telephone.

Regime troops stormed a Damascus district with tanks on Thursday for the first time, five days on from the outbreak of fierce clashes in the capital, the Syrian Observatory for Human Rights said.

"The army stormed the Qaboon district with a large number of tanks," the Observatory's Rami Abdel Rahman told Agence France Presse. "This is the first time that tanks enter a Damascus district."

Syrian state television broadcast images on Thursday of President Bashar Assad in a meeting with the new defense minister, Fahd al-Freij.

This was the first public sighting of Assad since a bomb attack in Damascus on Wednesday killed three top regime officials, including Freij's predecessor, Daoud Rajha.

The EU is preparing to freeze the assets of 26 Syrians close to President Bashar Assad while readying plans to board vessels and planes suspected of transporting arms for his regime, diplomats said Thursday.

The diplomats told Agence France Presse that foreign ministers from the 27-nation bloc were likely to agree at talks on Monday to inspect planes and ships believed to be carrying arms or goods used by the Damascus regime to put down protests.

Russia and China on Thursday vetoed a U.N. Security Council resolution that would threaten sanctions against Syria's President Bashar Assad if he does not end the use of heavy weapons.

The third Russia-China veto in nine months opened up an acrimonious battle at the 15-nation council over who is to blame for the world powers' failure to get international action to halt the Syria conflict.

Syrian President Bashar Assad's mother and sister have gone to Tartus province for the funeral of his brother-in-law Assef Shawkat who was killed in Wednesday's Damascus bomb, a security source told Agence France Presse.

"Anissa Assad, the widow of (ex-president) Hafez al-Assad and her daughter Bushra traveled on Wednesday evening along with several women from their entourage to Latakia and they then made their way to Tartus," the source said.