Syria's main opposition group, the High Negotiations Committee (HNC), has threatened to boycott the next round of peace talks unless the government stops its bombing campaign and the situation on the ground improves.
George Sabra, a member of the Syrian opposition delegation, the HNC, said on Wednesday that "while real steps aren't taken on the ground in Syria, the participation of the delegation of the HNC will remain suspended".
The HNC left formal negotiations last week when at least 40,000 Syrians fled fighting near Aleppo after government forces continued an offensive against opposition fighters there.
At least 35 people, including eight children were killed in Aleppo on Tuesday in attacks carried out by the government, a monitoring group said.
Following a lull in fighting after the ceasefire took effect on February 27, violence has intensified in recent days, with at least 100 civilians killed in air strikes, shelling and rocket fire since Friday.
When asked on Wednesday whether a new date had been set, Sabra said it was up to the United Nations to say when peace talks would resume, pointing out that the opposition would not take part until its demands were met.
TALK TO AL JAZEERA: Staffan de Mistura says no 'plan B' for Syria
The UN said on Wednesday that no date had been set, but projected that talks could resume between May 14 and 15, stressing that the dates were "very, very theoretical".
Speaking on anonymity, a Western diplomat told Reuters that it was "not at all a given that the two parties will return to Geneva.
"[UN Special Envoy, Staffan de Mistura] feels that ending the round without giving a date for the next one would not be a good sign."
The diplomat's remarks contradicted an earlier statement by Russia's Deputy Foreign Minister Mikhail Bogdanov that talks would resume in Geneva on May 10.
Bogdanov's comments were reported earlier on Wednesday by the RIA news agency, but a spokeswoman for de Mistura said in an email that May 10 was speculation.
Fighting in Syria has killed more than 250,000 people and displaced almost half the country's prewar population of 23 million.
Source: Al Jazeera