The announcement came on the same day as the United Nations said it wanted to start a fresh round of peace talks between Syrian factions on July 10 in Geneva.
The Syrian regime declared a 48-hour ceasefire in the southern city of Daraa from Saturday, as mediators announced two separate attempts to convene new peace talks next month.
The regime's general command said the truce went into effect at noon local time "in support of local reconciliation efforts". The announcement came on the same day as the United Nations said it wanted to start a fresh round of peace talks between Syrian factions on July 10 in Geneva, and Russia said it hoped to hold talks in Kazakhstan's capital Astana on July 4-5.
The Syrian Observatory for Human Rights, a Britain-based monitor of the war, reported a cautious calm in the hours after the truce was announced.
Deraa is among the areas included in a "de-escalation zones" deal brokered by Russia, Iran and Turkey earlier this year.
But recent weeks have seen heavy clashes in Daraa city and the surrounding area, with civilians among those caught in the fighting and bombardment.
Rebels control around 60 percent of Daraa city, and the province as a whole is one of the last remaining bastions of opposition forces in the country.
In Washington, the US State Department said "we welcome any initiative to reduce tensions and violence in southern Syria".
It urged Damascus "to live up to its own stated commitment during this ceasefire initiative".
"The opposition should similarly halt attacks to allow the ceasefire to endure, and hopefully be extended," the statement added.
There was no immediate official confirmation that the opposition agreed to the truce.
Syrian regime has pursued a series of so-called "national reconciliation" agreements with rebels in different parts of the country, including recently near the capital.
Under the deals, rebels who surrender are generally offered safe passage to opposition-held territory elsewhere in the country.
The opposition criticises the deals as a "starve or surrender" tactic, saying they are forced into the agreements after heavy regime bombardment or siege. But the regime has touted the deals as the best way to end the six-year war.