In Amman, Jordan, he said the temporary truce could be a first step in helping Syrians "to resolve their problems and to rebuild a new Syria."
The Syrian government said it wants a cease-fire but the rebels lack a unified leadership that can agree to it.
Both sides have flouted previous cease-fires after verbally agreeing to them.
Iranian President Mahmoud Ahmadinejad, a close ally of Assad, called for the truce during a visit to Kuwait. The Iraqi government also expressed its support in a statement, calling on all sides to abandon violence "to save the region from more miseries and pains."
Activists say more than 33,000 people have been killed since the anti-Assad uprising started in March 2011.
Also Thursday, Syria's state news agency said rebels blew up two oil and gas pipelines in the northeast near the Iraqi border. The agency, SANA, said the attack hit one oil and one gas pipeline near the city of Deir al-Zour. The pipelines ran between Deir al-Zour and the city of Palmyra in central Syria.
SANA quoted an oil ministry official saying the lines were immediately shut off, the fires were extinguished. Rebels have repeatedly bombed such pipelines.
Associated Press writers Ali Akbar Dareini in Tehran, Iran, Jamal Halaby in Amman, Jordan, and Sameer N. Yacoub in Baghdad contributed reporting.
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