The first direct negotiations between the Syrian government and rebels seeking to overthrow President Bashar al-Assad are to be held on Saturday after the sides refused to sit down together on the first day of a negotiation process billed by the international community as the only way to end the country's bloody crisis.

Lakhdar Brahimi, the veteran Algerian mediator, announced on Friday night that the parties had agreed "to meet in the same room" after a day of frantic efforts at UN headquarters in Geneva to prevent either side from walking out. "Nobody will be leaving on Saturday and nobody will be leaving on Sunday," he told a press conference.

The first threat to quit came from the Syrian foreign minister, Walid al-Moualem, who warned on Friday morning that he would return to Damascus unless "serious talks" were held by Saturday.

Brahimi met government and opposition negotiators separately behind closed doors at the Palais des Nations while outside their respective representatives blamed each other for the apparent deadlock. But it was unclear whether a face to face meeting had ever been guaranteed on the first day. Talk of the collapse of the negotiations was premature.

Discussions had been encouraging, Brahimi said. "We never considered that would be an easy process. In our business certainty is a very rare commodity. But I think the two parties understand what is at stake. Their country is in very bad shape. The huge ambition of this process is to save Syria. No less than that. So wish us luck."

Opposition spokesmen had said they would not start talks until the other side accepted the Geneva I agreement of 2012, which calls for the creation of a transitional governing body in Damascus by mutual consent. Given that the rebels insist Assad must go – and Assad is adamant that he will not – it remains hard to see how that can happen.

Moualem and other Syrian government officials have emphasised the need to discuss "terrorism", their blanket term for opposition to Assad, before talks on a political solution to the 34-month crisis, which has claimed an estimated 130,000 lives, and made 2 million people refugees and Syria a magnet for al-Qaida-inspired extremists.

Brahimi's upbeat tone was echoed by other officials. "It is difficult," a European diplomat said. "But that was only to be expected as they are getting close to the real issues." A US source said: "This is the beginning of a negotiation process. Expect lots of ups and downs. What is important is that the process in Geneva continues."

Agreement to meet on Saturday suggested that neither side wanted to be blamed for walking out, at least at this early stage. Al-Arabiya TV quoted an unnamed Syrian source as saying that the government had agreed to release more than 5,500 prisoners. If confirmed, that would be a significant confidence-building measure.

Brahimi said there would be discussion of improving access for humanitarian aid and ending violence. But he added: "Talking about it doesn't mean resolving it."

Amid all this diplomatic activity it was hard to avoid a sense of disconnect from the crisis on the ground. The pro-opposition Syrian Observatory for Human Rights reported that 63 people had now died due to poor health and living conditions in the besieged Yarmuk Palestinian area of Damascus. "Dear Geneva II crowd: Could you please get people in Homs and Yarmouk some food?" one activist tweeted. Air raids were reported over Aleppo.

Oxfam said in a statement: "Today has seen important progress and it is vital that a sense of urgency continues to underpin these talks. Every second counts here in Geneva as each day millions of Syrians are suffering as the conflict tears their country apart."

Anti-Assad demonstrators protested in the winter sunshine outside the UN building as the consultations, spin and rumour swirled inside.

Beyond any immediate expectations, Syrian opposition supporters say they fear being drawn into a long "process" that creates an appearance of efforts to end the crisis while a grim and violent reality becomes routine.

"We Syrians don't want to become like the Palestinians after the Madrid conference or the Oslo agreement and become an 'issue' that lasts for years without ever being resolved," said Ghassan Abboud, an exiled businessman. "We just want to live our lives, and we don't want a president who attacks us with chemical weapons and Scud missiles."

Iran's foreign minister, Javad Zarif, meanwhile called for all "foreign elements" to leave Syria – presumably a reference to foreigners who are fighting with the rebels. Iran is one of Assad's closest allies and has been widely criticised in the west for backing Syria and supporting Lebanon's Hezbollah militia, which is battling on the government's side. It was disinvited by the UN from the 40-nation Montreux conference on Wednesday after refusing to sign up to the Geneva I principles. John Kerry, the US secretary of state, said at the World Economic Forum in Davos that the Syrian opposition would go on fighting as long as Assad remained in power.