* All allegations must be investigated, Ban says
* Damascus says broader probe would violate sovereignty
* Issue divides Russia and Western powers
* Advance team in Cyprus awaits go-ahead from Damascus (Adds reaction from Damascus)
An advance team of U.N.-mandated experts has gone to Cyprus and is awaiting permission from the Syrian government to investigate allegations of chemical weapons attacks, U.N. Secretary-General Ban Ki-moon said on Monday.
Syria has asked the United Nations only to investigate what it says was a rebel chemical attack near Aleppo. The opposition blames President Bashar al-Assad's forces for that strike and also wants the U.N. team to look into alleged chemical attacks by the government side elsewhere.
Syria's ally Russia has backed Damascus against demands from Western powers that the investigation be widened. Ban made clear he wanted an all-encompassing inquiry, saying it was the "firm principle" of the United Nations that investigators be granted access to all areas where chemical weapons were allegedly used.
After meeting the head of the Organisation for the Prohibition of Chemical Weapons (OPCW), which is providing scientists and equipment, in The Hague, Ban said an advance team was in Cyprus, ready to go to Syria within 24 hours.
"All we are waiting for is the go-ahead from the Syrian government to determine whether any chemicals weapons were used, in any location," Ban said.
"I urge the Syrian government to be more flexible, so that this mission can be deployed as fast as possible," he said.
Syria's Foreign Ministry compared efforts to broaden the probe to the U.N.'s role in the run-up to the invasion of Iraq by the United States.
It is "at odds with the Syrian request. It shows there are hidden intentions...which violate Syrian sovereignty," a statement on state television said. "Syria cannot accept these manoeuvres."
Ahmet Uzumcu, head of the OPCW, said the full mission would comprise 15 experts, including inspectors, medical experts and chemists. Officials from the Geneva-based World Health Organisation will also be on the team.
It will be headed by Swedish scientist Ake Sellstrom, a former U.N. weapons inspector in Iraq, whom Ban also met in The Hague. Sellstrom was to join the advance team on Monday.
An offer of assistance came from opposition campaigner Basma Kodmani, who told Sellstrom in an undated letter that tissue samples had been gathered from six alleged victims of chemical attacks on 24 March in the villages of Adra and Ateybeh.
"There are 32 persons showing symptoms of illness and are currently being treated following exposure to the weapons who are willing to be examined by the inquiry," the letter said.
Ban said all serious claims on the use of chemical weapons in Syria should be examined, and urged speed so that evidence was preserved.
"The use of chemical weapons by any side, under any circumstances, would constitute an outrageous crime with dire consequences," he declared.
Britain and France want to broaden the U.N. investigation to include Homs and Damascus, where rebels say Assad's forces used chemical munitions. They also blame the government for the incident near Aleppo.
Russia, which has used its veto-wielding seat on the U.N. Security Council to counter Western pressure on Syria, has suggested that Western powers are using the spectre of weapons of mass destruction to justify intervention in Syria, as they did in Iraq.
The OPCW, established to oversee the 1997 Chemical Weapons Convention, has helped to destroy roughly 80 percent of chemical weapons stockpiles declared by 188 members.
Syria is one of just eight countries not to have joined, along with Angola, Egypt, Israel, Myanmar, North Korea, Somalia and South Sudan.
Western intelligence agencies say Syria is believed to have one of the largest remaining stockpiles of undeclared chemical weapons in the world, making it a security issue for Washington and its European allies, as well as for neighbouring Israel.
Syria has not confirmed or denied possessing chemical weapons, but says that if it did, it would never use them against its own people, only to repel foreign invaders.