“I have indicated from the first day I won't talk for the sake of talking,” de Mistura said.
“I therefore have taken the decision to bring a temporary pause,” he said.
“Both sides indicated they are interested in having the political process started. I have already fixed a date for the next talks of 25th February.”
His comments came after several days of fruitless talks aimed at starting indirect negotiations between the Syrian government and opposition.
The hoped-for six months of indirect “proximity talks” are part of an ambitious roadmap agreed by outside powers embroiled in the conflict in November in Vienna.
The opposition umbrella group High Negotiations Committee (HNC) only reluctantly arrived in Geneva on Saturday, a day after representatives from President Bashar al-Assad.
The HNC was insisting on immediate steps including humanitarian aid getting through to besieged cities, a halt to the bombardment of civilians and the release of prisoners.
It was also outraged that while in Geneva a major offensive by the Syrian army and allied militias was happening on the ground near Aleppo, backed by intense Russian air strikes.
In a major blow to the rebels, a military source said Wednesday that President Bashar al-Assad's army had cut the last supply route linking opposition forces in Aleppo to the Turkish border.
The government delegation meanwhile complained that the HNC was disorganized, had not named its negotiators and that the body contained individuals it considered “terrorists”.
De Mistura said he was asking for the International Syria Support Group (ISSG) of outside countries to convene “as soon as possible.”
The almost five-year-old civil war has killed more than 260,000 people, forced millions from their homes and sucked in a host of regional and global powers.
Hijab, a former Syrian premier who defected in 2012, went straight to a Geneva hotel to meet other members of his High Negotiations Committee (HNC).
An AFP reporter said that de Mistura also arrived at the hotel, with an opposition source telling AFP saying he was there to meet Hijab informally.
Hijab's arrival was seen as a potentially positive sign because of the weight he carries with the HNC, a Saudi-backed opposition alliance that is opposed to President Bashar al-Assad.
The Syrian government accuses the HNC of being “not serious” and of containing figures from armed rebel groups whom Damascus and its backer Russia consider “terrorists”.
One such person is Mohammed Alloush, a leading member of Islamist rebel group the Army of Islam, in Geneva since Monday and nominally the HNC's chief negotiator.
“The problem is not with de Mistura. The problem is with the criminal regime that decimates children and with Russia which always tries to stand alongside criminals,” Alloush told reporters Wednesday, clutching a photo of a young boy he said was severely wounded by Russian air strikes
De Mistura said on Monday after his first formal talks with the HNC that a hoped-for six months of indirect talks between the government and the opposition had begun.
But this declaration proved to have been premature, with the chief government negotiator rejecting that this was the case and the HNC cancelling a meeting with de Mistura on Tuesday in anger at Russian air strikes in Syria.
“With Hijab here, the HNC can better demonstrate a unified position in representing the opposition,” a Western diplomat said in Geneva on condition of anonymity.
“This is a very complicated process and it's going to require all the actors to remain in constant dialogue,” the diplomat said.