Otri submitted his resignation on Tuesday. Assad, however, appointed him as the caretaker premier pending the formation of a new government, the Syrian Arab news agency (SANA) reported.
The decision to leave office came after weeks of protests calling for reforms, which led to deadly violence in several cities.
The opposition accuses security forces of being behind the killings. But the government denies the allegation and blames armed gangs and foreign powers, especially Israel, for the unrest.
Supporters of Syrian President Bashar al-Assad staged rallies across the country to shore up a leader facing the strongest challenge since he came to power 11 years ago.
State-run television showed live footage of hundreds of thousands pouring onto the main streets of Damascus, Aleppo, Hama and al-Hassakah today.
The pro-regime marches are a response to protests in several Syrian cities and towns since mid-March to demand political reforms, including an end to a 48-year-old emergency law. More than 90 people were killed as the government cracked down on dissent, according to unconfirmed reports cited by Amnesty International.
Syria is the latest country in the region to be hit by the wave of uprisings that ousted longtime rulers in Egypt and Tunisia, and sparked armed conflict in Libya. Assad’s regime is an ally of Iran and a power broker in neighboring Lebanon, where it supports the Shiite Muslim Hezbollah movement.
“The rallies today were organized by non-governmental organizations that support President Assad and the government,” George Jabbour a member of parliament said in a telephone interview from Damascus today.
On Monday, Vice President Farouk al-Shara announced that President Assad planned to deliver an important speech within the next two days.
The Syrian head of state is expected to reach out to all Syrians in his speech and reassure them of reforms in the country’s political system.