The announcement was accompanied by the agency's call for $295 million more in funding, money it says is necessary to provide humanitarian aid to the ever-increasing number of Syrian refugees pouring into neighboring Turkey, Jordan, Lebanon and Iraq.
"This plan provides for up to 700,000," Panos Moumtzis, UNHCR refugee coordinator, said in a news briefing.
Since the Syrian civil war between President Bashar al-Assad's regime and the various factions of the Free Syrian Army began 18 months ago, about 294,000 refugees have fled the violence.
The World Food Program's Regional Refugee Emergency Coordinator Edward Kallon said, "Humanitarian needs, especially food, are growing, as thousands more Syrians pour into neighboring countries."
Yesterday was, according to the UK-based activist group the Syrian Observer for Human Rights (SOHR), the deadliest day in the conflict - 304 people died. SOHR said 199 were civilians.
Rami Abdel Rahman, director of the Syrian Observatory for Human Rights said the number is likely higher.
"If we count the unidentified bodies, the figure will be much higher," he told the BBC.
Activists estimate about 27,000 people have died since conflict began.
Calls for intervention continue, but action seems unlikely at this point. On Wednesday US Secretary of State Hillary Clinton said the UN Security Council was "paralyzed," and urged its members to reach an agreement that would help end the violence.
"The atrocities mount while the Security Council remains paralyzed and I would urge that we try once again to find a path forward," she said.