The European Union on Friday reiterated a request to Damascus to enable a U.N. chemical weapons probe in Syria after the United States said for the first time that the regime has probably used such weapons.

"We hope there will be a United Nations investigation inside Syria to hopefully shed some light on what has really happened," a spokesman for the EU's top diplomat Catherine Ashton said after being queried over the EU stand.

Secular-leaning judges have set up a more liberal alternative to sharia law courts in Aleppo but face an uphill battle for influence as Islamist groups shore up support in rebel-held Syria.

The sharia courts have the backing of an array of hardline rebel groups whose fighters help enforce their decisions in rebel-controlled districts of Syria's main northern city.

The number of Syrians who have fled their conflict-ravaged homeland has surpassed 1.4 million, the United Nations refugee agency said Friday, warning that it was no longer able to meet their medical needs.

As of Thursday, the total number of Syrians registered as refugees was 1,401,435, the UNHCR said.

Syria's opposition on Friday urged the U.N. Security Council to take immediate action after the United States said for the first time the regime probably used chemical weapons.

"It is time for the U.N. Security Council to act" on Syria, an official from the main opposition National Coalition told Agence France Presse.

The international community must be ready to use military action in response to any chemical weapons use by the Syrian regime, Israel's deputy foreign minister said on Friday.

"From the moment the international community understands that red lines have been crossed and that chemical weapons have been used, they will realize there's no other choice than to react (militarily)," Zeev Elkin told Israeli army radio.

British Prime Minister David Cameron said on Friday that growing evidence of the use of chemical weapons by the Syrian regime was "extremely serious".

He agreed with U.S. President Barack Obama that such use would represent a "red line" for the international community, but said the response would likely be political rather than military.

Russian Deputy Foreign Minister Mikhail Bogdanov handed over on Friday to President Michel Suleiman a letter of support from his Russian counterpart Vladimir Putin.

Putin hailed in the letter to the efforts exerted by Suleiman to maintain stability in Lebanon, expressing support to the resumption of the all-party talks and to the dissociation policy adopted by the Lebanese government.

Fresh fighting erupted on the outskirts of Damascus on Friday, as Syrian regime troops battled rebels in the north, south and east, backed in some areas by tanks and militia, a watchdog said.

"Fierce clashes are raging in Barzeh district, pitting rebels against troops and members of the pro-regime popular committees," the Syrian Observatory for Human Rights said.

U.N. leader Ban Ki-moon on Thursday renewed an "urgent call" for Syria to let inspectors into the country after the United States said government forces had probably used chemical weapons.

"The secretary general has consistently urged the Syrian authorities to provide full and unfettered access to the team. He renews this urgent call today," said U.N. spokesman Martin Nesirky.

Britain has "limited but persuasive" evidence of the use of chemical weapons in Syria, including sarin gas, the Foreign Office said on Thursday, following similar comments by U.S. officials.

"We have limited but persuasive information from various sources showing chemical weapon use in Syria, including sarin," a Foreign Office spokeswoman said.