UNITED NATIONS - The four European members of the Security Council -- Britain, France, Germany and Portugal -- said here Thursday that they would begin working on a Security Council sanctions resolution on Syria.

"We believe that the time has come for the council to take further actions to step up the pressure against those who are responsible for the violence against the citizens of Syria," said Philip Parham, British deputy permanent representative to the UN after a closed-door meeting on Syria at the Security Council.

"So we will be working on a Security Council resolution which will include measures to apply that pressure to those that are responsible and we will be discussing that resolution with our colleagues on the council over the coming days," he told reporters outside of the Security Council chamber.

The German, French and Portuguese envoys echoed his remarks.

The United States would support further action in the Security Council through a resolution, US deputy permanent representative Rosemary DiCarlo said.

US President Barak Obama Thursday for the first time explicitly urged Syrian President Bashar al-Assad to step down, imposing the harshest sanctions on Syria to date.

Also on Thursday, French, German and British leaders called for further sanctions against Syrian authorities on the European level, quoting that Syrian President Assad has lost "all legitimacy" and should step down from power.

In response, Syrian UN Ambassador Bashar Ja'afari told reporters that the United States and other western members in the Security Council are waging a "diplomatic and humanitarian war" against Syria.

"It is really pitiful and unacceptable to hear from seasoned diplomats in charge of important questions pertaining to maintaining peace and security ... really pitiful to see these influential countries in the council, making use of the council as an instrument to fulfill their illegitimate strategies against my own country as well as against the whole area," Ja'afari said.

"There is no concrete outcome (of the meeting), because thank god we still have wise guys inside this council who do have different information and who do have contradictory information and who do have solid and credible reports," he said.

When asked if he could confirm remarks that President al-Assad told UN Secretary-General Ban Ki-moon in a phone conversation Wednesday that Damascus had ended all military operations.

He said it was "already a fact on the ground, the military and police operations stopped in Syria."

Syria has been in unrest since mid March when anti-government protests broke out in the southern province of Daraa and spread to other cities.

The Syrian authorities blamed the unrest on "armed groups and foreign conspiracy" and stressed that it would track down gunmen who have intimidated people and damaged public and private properties.

Russia and China, as permanent members of the 15-member council who have the right to veto, opposed tough measures against Syria. Brazil, India and South Africa, non-permanent member of the council, also went against sanctions on Syria.