However, special envoy Staffan de Mistura admitted discussions over who should take part were continuing.
The priorities were to bring about a broad ceasefire, stop so-called Islamic State (IS) and increase aid, he said.
Mr de Mistura's announcement came as 23 people were reportedly killed in an attack on a rebel checkpoint in Aleppo.
A suicide bomber driving a fuel lorry targeted a checkpoint run by the Islamist rebel group Ahrar al-Sham, the Syrian Observatory for Human Rights said.
Four of the group's commanders and four civilians were believed to be among the dead, according to the UK-based monitoring group.
It is not known who carried out the attack, in which dozens of people were also wounded.
More than 250,000 people have died in Syria in the almost five years of fighting since opposition protests against the rule of President Bashar al-Assad began.
Civilians under siege
International system has failed Syria
The story of the conflict
Mr de Mistura said the "proximity talks" would be indirect to start with, with negotiators ferrying messages between representatives of the warring parties.
The talks had been delayed by disputes over who should attend, he said, but he added that he expected invitations to be sent out on Tuesday.
Participation by IS and the al-Qaeda's affiliate in Syria, al-Nusra Front, had been ruled out, he said, but discussions about other rebel groups were continuing.
Turkey has warned that participation by Syrian Kurdish forces, which it considers to be "terrorists", could cause the talks to fail.
Mr de Mistura said the first phase of negotiations would last between two and three weeks.
He warned the talks would be stormy, with "a lot of posturing, a lot of walk-outs and walk-ins".
Issues of governance, a constitutional review and future elections would also be on the agenda, he added.
Talks aimed at finding a political solution to the war in Syria are expected to start in Geneva on Friday and last six months, the UN has said.