The negotiations, to be held in the Kazakh capital Astana, are intended to build on a ceasefire in effect since late December, brokered by regime ally Russia and rebel backer Turkey.
The truce has brought quiet to large parts of the country, but has been threatened by continuing violence, particularly near the capital Damascus.
Overnight and into Wednesday, government warplanes hit opposition areas in the provinces of Aleppo and Idlib, as well as the Eastern Ghouta region near the capital, the Syrian Observatory for Human Rights said.
The strikes on the town of Taftanaz killed three rebels from an Islamist group allied to the jihadists, the Britain-based monitor said.
An AFP correspondent in the town saw a building that had totally collapsed in the attack. The White Helmets, a rescue service operating in rebel areas, spent hours clearing debris with picks and hammers.
Government air strikes also hit Eastern Ghouta this morning, the Observatory said.
The rebel-held region has been hit by artillery fire during the truce, but the air strikes, which killed a woman and wounded nine other people, were the first since the start of the ceasefire, the monitor said.
The rebel-held region some 15 kilometres northwest of Damascus is the main water source for the capital, but supply has been cut since December 22.
Some 5.5 million people in Damascus and its suburbs are suffering water shortages as a result, the UN says.
The government accuses rebels, among them Fateh al-Sham, of deliberately cutting the supply.
The rebels say regime strikes damaged pumping facilities and deny that Fateh al-Sham, previously known as Al-Nusra Front, has forces in the area.
"The role of the Syrian army is to liberate that area in order to prevent those terrorists from using that water in order to suffocate the capital," Assad told French media on Monday.
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