Britain and France on Wednesday renewed their call for Syrian President Bashar al-Assad to go, after a suspected chemical weapons attack by Damascus killed scores of people in a rebel-held area.
Foreign ministers Boris Johnson of Britain and Jean-Marc Ayrault of France spoke during an international conference on Syria, which the European Union convened in Brussels in a bid to shore up stalled peace talks between Assad and his rivals.
"This is a barbaric regime that has made it impossible for us to imagine them continuing to be an authority over the people of Syria after this conflict is over," Johnson said.
Ayrault said the attack was a test for the administration of US President Donald Trump.
The future of Assad, who is backed militarily and politically by Russia and Iran, has been the main point of contention blocking progress in talks. The war has raged for more than six years, killing 320,000 people, displacing millions and leaving civilians facing dire humanitarian conditions.
"The need for humanitarian aid and the protection of Syrian civilians has never been greater. The humanitarian appeal for a single crisis has never been higher," United Nations' Secretary General Antonio Guterres said.
The UN has called for $8 billion this year to deal with the crisis and the Brussels gathering was due to come up with fresh pledges of aid.
Hours before the UN Security Council meets over a resolution proposed by Washington, London and Paris on the attack, Guterres said: "We have been asking for accountability on the crimes that have been committed and I am confident the Security Council will live up to its responsibilities."
The three countries blamed Assad for the attack. Russia said it believed the toxic gas had leaked from a rebel chemical weapons depot struck by Syrian bombs, setting the stage for a diplomatic collision at the Security Council.
In condemning Assad, Trump did not say how he would respond. The attack came a week after Trump's Secretary of State Rex Tillerson and UN envoy Nikki Haley said their focus was on defeating Islamic State in Syria rather than pushing Assad out.
"Under Obama, we agreed that Assad had to go, but now it is unclear where the Trump position lies," said a senior EU diplomat.
On the aid front, Germany pledged 1.2 billion euros ($1.28 billion) for 2017 on top of its previous commitments. London offered an additional one billion pounds ($1.25 billion).
The EU and its members have so far mobilised about 9.5 billion euros in Syria emergency humanitarian aid, Brussels says.
The bloc says it will withhold development aid and not pay for any reconstruction if Damascus and its backers wipe out Syria's opposition and moderate rebels, regaining full control of the country but denying its ethnic and religious groups political representation.
"But behind this line, there are divisions in the EU on Assad. Some are hawkish, some others want to think whether we could work with him somehow," another senior EU diplomat said.
"The EU's internal splits only add up to those among the big players in this war. There is a sense of despair but the international community just cannot agree on how to fix Syria."