Evidence points that the regime of Syrian President Bashar al-Assad used chemical weapons in an attack near Damascus last month, EU defence ministers have concluded.

"There are many signs that the regime used the (chemical) weapons," Lithuanian Defence Minister Juozas Olekas said as EU counterparts met in the Baltic state, which currently holds EU's rotating presidency.

Olekas said that although all his fellow ministers "condemned the use of chemical weapons and believed those responsible must be held accountable" there were "a variety of opinions" on what should be done in response.

Another EU official who spoke on condition of anonymity said France and Denmark were among the most vocal supporters of military intervention against the Assad regime, while Italy and Spain remained more sceptical.

"However, no one said that they would condemn it if there is military action," the official told AFP.

EU foreign ministers are also due to discuss Syria at their meeting in Vilnius on Friday, with US Secretary of State John Kerry due to join the talks on Saturday.

NATO chief Anders Fogh Rasmussen said a firm international response was needed to Syria.

"The international community has a responsibility to uphold and enforce the international ban against the use of chemical weapons," he told reporters on Friday.