* France holds ministers meeting - US, Saudi attend
* Formin Juppe says U.N. mission needs 300-400 observers
* Sarkozy renews call to set up humanitarian corridors
* Moscow declines invite, says meeting “destructive”
By John Irish and Daniel Flynn
PARIS, April 19 (Reuters) - France said on Thursday a U.N.-backed peace mission needed to send at least 300-400 observers to Syria to succeed - higher than previous estimates - adding foreign powers would discuss new ways to end the violence in case the mission failed.
Damascus and the United Nations agreed on Thursday on the terms for observers to enter the country to monitor a ceasefire, called more than a year after the start of an uprising against President Bashar al-Assad.
But many Western powers remain skeptical the mission will have the clout it needs. U.N. Secretary General Ban Ki-moon earlier said the Syrian government had not fully withdrawn troops and heavy weapons from towns, as it had promised in a six-point plan to end the conflict and begin a political transition.
“The objective is to ask whether we can deploy an observer mission that is efficient, meaning numerous ... at least 300-400 to cover the country,” French Foreign Minister Alain Juppe told reporters ahead of a meeting of foreign ministers gathered in Paris on Thursday under the banner of “Friends of Syria”.
“If that is not possible in a certain time frame, we need to look at other measures to end the massacres,” he said.
Juppe’s estimate of the number of observers required was above the 250 which Syrian Foreign Minister Walid al-Moualem had said was “reasonable” and the 300 which Ban earlier said was necessary to monitor the shaky ceasefire.
The government of President Nicolas Sarkozy, who faces the first round of a tough re-election battle on Sunday, has long led calls for Assad to step aside and was the first country to recognise the opposition Syrian National Council as a legitimate interlocutor.
Juppe said Paris had absolutely no trust in the Syrian leader or his government. While a truce worked out by international envoy Kofi Annan has held in some parts of Syria, the army has kept up attacks on rebels in several opposition areas.
The Syrian government says it is under attack from armed “terrorist groups”.
“I am convinced that if there are several hundred observers, allowed to move around freely, and if Syria allows foreign media into the country, then things will drastically and fundamentally change,” said Juppe.
Ahead of the meeting - attended by United States, Turkey, Qatar, Saudi Arabia and other nations - Sarkozy repeated calls to create a safe passage for relief organisations to get food and medicine to about 1 million civilians caught up in the fighting.
“Bashar al-Assad is lying ... He wants to wipe Homs off the map just like (former Libyan leader Muammar) Gaddafi wanted to destroy Benghazi,” Sarkozy told Europe 1 radio.
“The solution is the establishment of humanitarian corridors so that an opposition can exist in Syria,” he said.
One diplomat in Paris for the meeting said there was no plan currently on the table for a humanitarian corridor or buffer zones.
“These options are being looked into in case of an unwanted eventuality. No decision has been made and in an ideal world they would need Security Council backing,” the diplomat said.
Under the French plan, aid would be funneled into Syria from its Mediterranean coast, an airport or from neighbouring countries including Turkey, Lebanon and Jordan.
“We will discuss the need to bring in humanitarian aid as part of (Annan’s six-point plan),” Juppe said. “Whether that is done through corridors or other ways is a technical point. What is key is to bring in aid.”
Russia, which was invited along with China to the Paris meeting, stayed away because the talks were “one-sided” without representation from the Syrian government, Russian Foreign Ministry spokesman Alexander Lukashevich said.
He added that Moscow deemed “Friends of Syria” as “destructive” and could undermine the U.N.-Arab League plan.
Sarkozy, who trails his Socialist rival in polls ahead of the first round of France’s presidential election on Sunday, said he was convinced that China and Russia would drop their support for Damascus if the international community showed unity and that Assad’s government would fall.
“The Chinese, like the Russians, do not like to be isolated and if we unite the major powers to say ‘this is the direction we must go in with our Arab allies’ then the isolation of China and Russia on this dossier will not last,” Sarkozy said.