"I have consistently emphasised the need to continue efforts in the Security Council," Ashton told members of the European Parliament.
Most European Union nations have consistently opposed calls by Britain and France to join US-led military strikes against President Bashar al-Assad, calling instead for a political solution and a UN role.
"The role of the Security Council is crucial and irreplaceable," Ashton said. "It is regrettable that the Council has been unable to reach agreement on how to shoulder its responsibilities with regard to the Syrian conflict."
"However we need to proceed with prudence and examine these developments," she said. "First and foremost the Syrian regime must agree to such an international action fully and without conditions."
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She also reiterated the EU stand that there was "no military solution" to the protracted conflict that began in March 2011, costing more than 110,000 lives.
Efforts to hold a peace conference, known as Geneva II, "must move ahead as soon as conditions permit," she said.
Delivering his annual "state of the union" speech before the European Parliament, Barroso said "the use of chemical weapons is a horrendous act that deserves a clear condemnation and a strong answer."
"The international community, with the United Nations at its centre, carries a collective responsibility to sanction these acts and to put an end to this conflict."
"The proposal to put Syria's chemical weapons beyond use is potentially a positive development," he added.
He recalled too that the 28-member bloc had been the world's leading aid donor since the two-and-a-half year conflict began, delivering almost 1.5 billion euros (USD 2 billion) in aid, of which 850 million were directly from the European Union budget.