Syria-based insurgents fighting the regime of President Bashar Assad on Thursday took to task their exiled leadership, in a stark show of divisions within the armed opposition.

"Nobody has the right to issue press releases, take decisions, or speak about operations in the Free Syrian Army's name, except for the FSA command inside Syria," the group's spokesman Colonel Qassem Saadeddine told Agence France Presse.

Syrian troops resumed their shelling of the Houla region on Thursday, killing at least one person at the site of a massacre of 108 people last week, the Syrian Observatory for Human Rights said.

"A boy was shot dead today by a sniper," Britain-based Observatory chief Rami Abdel Rahman told Agence France Presse.

Portugal has declared Syria's Paris-based ambassador Lamia Shakkur persona non grata, following a wave of sanctions by Western countries against Syrian diplomats, the foreign ministry said Thursday.

Shakkur, who also represented Damascus in France and Switzerland, has already been ordered to leave by Paris and declared persona non grata by Bern, in the wake of the recent massacre at Houla in central Syria.

A Syrian honorary consul in the United States has resigned in protest after last week's killings in Houla, where more than 100 people were slaughtered in a massacre blamed on pro-government forces.

The resignation of Hazem Chehabi, who had helped arrange passport and other services in California, came as several countries expelled Syrian envoys to protest the spiraling violence of the 14-month government crackdown.

The head of Iran's powerful Revolutionary Guards on Thursday made a pointed visit to three islands in the Gulf whose ownership is fiercely disputed by Tehran and the United Arab Emirates (UAE).

Guards Commander Mohammed Ali Jafari, accompanied by his naval commander, Ali Fadavi, went to the islands of Abu Musa, Greater Tunb and Lesser Tunb to deliver a speech stressing they were Iran's "strategic and sensitive territory," the Guards' official news website said.

U.S. Secretary of State Hillary Clinton on Thursday criticized Russia's resistance to U.N. action on Syria, warning that its policy could contribute to a civil war.

The Russians "are telling me they don't want to see a civil war. I have been telling them their policy is going help to contribute to a civil war," she told a mainly student audience on a visit to Copenhagen.

U.N. chief Ban Ki-moon warned Thursday of a "catastrophic civil war" in Syria after the massacre of more than 100 civilians in the town of Houla that sparked global horror and outrage.

"The massacres of the sort seen last weekend could plunge Syria into a catastrophic civil war, a civil war from which the country would never recover," he told an Istanbul forum of the U.N.-led Alliance of Civilizations initiative.

President Vladimir Putin warned Thursday that Russia's position on Syria would not shift under pressure despite the crisis likely topping the agenda during his upcoming visits to Berlin and Paris.

"Russia's position is well-known. It is balanced and consistent and completely logical," Interfax quoted Putin's spokesman Dmitry Peskov as saying.

Two U.S. tourists have been kidnapped in Egypt's Sinai peninsula by Bedouins protesting the arrest of one of their tribesmen on a drugs charge, a security official said on Thursday.

The tourists were abducted late on Wednesday near the resort of Dahab on the Red Sea, the official said, adding that talks were under way in a bid to secure their release.

A senior Kuwaiti official has slammed Iran for criticizing a Kuwaiti court ruling that sentenced four men to life in jail for spying for Tehran, newspapers reported on Thursday.

"Unfortunately, this is an act of disrespect for Kuwaiti court rulings that we highly appreciate and respect," foreign ministry undersecretary, Khaled al-Jarallah, was quoted as saying by Al-Rai newspaper.