United Nations envoy Staffan de Mistura has warned not to expect "miracles" as a new round of UN-backed talks between rival sides in Syria's conflict resumed amid ongoing fighting across the country.

As rebel fighters in Syria pushed on with a major offensive against government forces in the central province of Hama, representatives of the two sides in the talks held in Geneva traded allegations over developments on the ground.

Syrian government envoy Bashar al-Jaafari accused the opposition of intentionally undermining the talks, saying an escalation of attacks over the past few days is "pushing everybody toward a total failure and fiasco in the political and diplomatic process".

For his part, Nasr al-Hariri, the Syrian opposition's chief negotiator in the talks, accused the government of targeting areas with civilians and carrying out arbitrary arrests.

READ MORE: The 'slow-motion slaughter' of Syrian civilians

On the agenda for the fifth round of the Geneva talks is governance - political transition, the constitution and elections - as well as counterterrorism at the request of Damascus.

Deadlock remains over most of the toughest issues, notably President Bashar al-Assad's fate, with the opposition insisting he cede power and the government declaring the subject off limits.

After a two-hour meeting with de Mistura, Jaafari said "terrorism" needed to be the priority.

In the opposite camp, Hariri said the opposition was committed to finding a political solution, but insisted such a deal could not include Assad.

"We reaffirm that we here to rid our country from terrorism and I say that Syria will not be free from terrorism of Daesh [ISIL] ... unless it is liberated first from the state terrorism practised by the regime," Hariri told reporters.

READ MORE: The voices missing from Syria's peace talks

The two sides are meeting separately with the UN.

"All of them have to talk about all four [issues]", de Mistura told reporters following the first full day of the round. "That is [the] deal."

De Mistura said he would aim to mesh the ideas shared on all subjects by both sides when the round ends next Friday.



"I am not expecting miracles, I am not expecting breakthroughs ... and I am not expecting breakdowns," the UN envoy said, reiterating that agreement on the agenda was itself a mark of progress.

De Mistura has recently been shuttling between Moscow, Riyadh, and Ankara, and talking directly with the United States, in preparation for the talks.

He urged the backers of separate talks in the Kazakh capital Astana - which involve Russia and Turkey and are supposed to guarantee a ceasefire - to resume more negotiations in an effort to bring the fighting to an end.

"Our expectation and strong suggestion to the guarantors to the Astana process that they do retake the situation in hand and that hopefully there will be new Astana meeting as soon as possible in order to control the situation, which at the moment is worrisome," he told reporters.

Fighting continues

In Syria, rebels were advancing in Hama province, as part of their biggest offensive against government forces in months.

The city of Hama remained under government control, but the opposition has gained ground in the countryside; rebels have seized 11 villages and several ammunition depots since Tuesday.

The UK-based Syrian Observatory for Human Rights monitor reported fresh violence on Friday, including shelling by government forces of areas in Sahl al-Ghab, northwest of Hama, and ongoing clashes in the countryside north of the city, as the army sought to retake territory and stop rebels from capturing a military airport.

Clashes also renewed in the capital, Damascus, witnesses earlier said.

Rebels fought with soldiers on the edge of the city centre in the Jobar district for a fifth day on Thursday.

Forces loyal to Assad's government conducted artillery and air strikes in a bid to restore control of positions they lost earlier this week, after surprise attacks by rebels in the northeast of the city.

Reporting from Geneva, Al Jazeera's Andrew Simmons said the talks were not off to a good start given the latest surge fighting in Syria.

"It's not a good start in the battlefield, in the sense that there is escalation, and it's not a good start here in terms of encouragement towards ... peace," Simmons said.

'Assad regime targeting schools, hospitals'

Earlier in the day, Hariri accused the government of not being committed to peace.

"I would like to remind you that since the beginning of the last round of talks, last month in Geneva, at least 11 schools have been targeted, in addition to at least 11 medical centres, including hospitals and makeshift clinics, and five markets by the Assad regime's air force and the countries that are supporting the regime."

Al Jazeera's Hashem Ahelbarra, reporting from Beirut, said that the rebels were aiming to put more pressure on the international community as they tried to bring about a political solution to the crisis.

"This is the first time in months that we've seen momentum being built by the rebels to take over ground, particularly in Hama," he said.

"[The rebels] are sending a clear message to the international community that, despite the fact that they lost Aleppo last year ... they can still change the reality on the ground."

Marwan Kabalan, an analyst at the Doha Institute's Arab Centre for Research and Policy Studies, told Al Jazeera that little had been achieved in the talks, which were entering their fifth round.

Kabalan said that the parties should be discussing four main themes - governance, fighting "terrorism", the constitution, and elections - but stressed that little was expected from this latest round.

"Most of the regional and international powers are not yet actually committed to solving this crisis," he said, adding that the US was focusing more on the fight against the Islamic State of Iraq and the Levant [ISIL, also known as ISIS] while Turkey's focus was on the actions of Kurdish groups in Syria.