The British and French foreign ministers say there are major obstacles to establishing safe zones for refugees within Syria, but that they are ruling out no measure yet.
French Foreign Minister Laurent Fabius and Britain's Foreign Secretary William Hague also announced greater aid for international relief efforts.
The two European diplomats were speaking ahead of a UN Security Council meeting on the growing humanitarian crisis in Syria. Turkey, which faces a growing influx of refugees, has urged world powers to consider setting up safe zones to protect Syrian civilians.
Hague, however, said such a plan would imply foreign military intervention. Hague and Fabius said the UN Security Council would be unlikely to give its agreement to any military operation to protect a safe zone.
Russia and China have vetoed three resolutions that could have led to economic sanctions against President Bashar al-Assad over the conflict and totally rejected any military intervention.
Call For Refugee Aid
A UN appeal for $373 million for relief operations for Syria and refugee camps outside the country has raised only $196 million.
Hague said other countries had to step up financial assistance to the United Nations and other aid groups.
"Today, the United Kingdom stands with France in calling for urgent and generous contributions from all nations to the United Nations relief effort," Hague said.
"One-and-a-half million people have been displaced inside Syria, 2.5 million are in need of urgent assistance, and the number of refugees in neighboring countries is growing day by day, today stands at over 200,000. And despite this desperate need the UN relief fund is only 50 percent funded."
Hague and Fabius said Britain will give an extra $4.75 million and France $6.2 million to aid efforts inside Syria and in camps in neighboring countries.
With reporting by AFP and Reuters