Beirut (AFP) - Syria's regime said Monday it would attend renewed peace talks in Geneva starting March 14, but the opposition was still considering whether to go despite a major lull in fighting.

The United Nations is hoping to restart peace talks that collapsed last month, building on a ceasefire that has led to the first significant decline in violence in Syria's nearly five-year civil war.

UN Syria envoy Staffan de Mistura has said he hopes talks can begin from Thursday, but officials have indicated it could take several days of preparations before they can start.

A source close to the Syrian regime delegation told AFP it would attend the new round of talks starting from March 14.

But the opposition has sent mixed signals, with the head of the Riyadh-based High Negotiations Committee, Riad Hijab, refusing to commit.

"The HNC will assess the situation in the coming days and we will take the appropriate decision," he said.

Hijab said a small HNC delegation would travel to Geneva "in the next two days" to meet the international task force monitoring the truce.

His statements appeared to be a step back from comments by HNC spokesman Riad Naasan Agha, who said the opposition delegation would arrive on Friday to take part in talks.

- Aid deliveries rise -

The truce between President Bashar al-Assad's regime and non-jihadist rebels is part of the biggest diplomatic effort yet to resolve Syria's conflict, which has killed more than 270,000 people and displaced millions.

Russia and the United States are on opposing sides of the conflict -- Moscow backs Assad and Washington supports the opposition -- but have made a concerted push for the truce and further peace efforts to succeed.

Observers say the partial truce, which does not apply to the Islamic State group or the Al-Qaeda-affiliated Al-Nusra Front, has largely held despite widespread scepticism before it took effect.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, said Sunday had been Syria's "calmest day" since the ceasefire began.

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Observatory chief Rami Abdel Rahman said the average number of daily civilian deaths had fallen by 90 percent since the truce came into force, with an 80 percent decline among soldiers and rebel forces.

Aid deliveries have also improved, with the UN delivering supplies on Monday to a key rebel bastion east of Damascus, the third distribution since the truce began on February 27.

World Food Programme spokesman Hussam al-Saleh said 22 trucks would distribute food, flour and medical supplies to Hammuriya, Jisreen and Beit Sawa in Eastern Ghouta.

Residents have taken advantage of the ceasefire to stage daily protests.

In Aleppo city, dozens of men demonstrated, carrying the three-starred tricolour of the uprising and banners reading: "The world's silence is louder than the barrel bombs of death."

But an anti-regime protest in northwest Idlib city ended abruptly after Al-Nusra fighters threatened to shoot demonstrators.

Moscow, which has provided a daily account of ceasefire violations, said the truce was still "in general" holding apart from unspecified "isolated provocations and shelling".

It said Russian planes were still carrying out strikes against IS and Al-Nusra in three provinces, including on the main IS stronghold of Raqa.

In September Russia began a campaign it says is targeting "terrorists", but has been accused of hitting non-jihadist rebels in support of Assad's forces.

- Vow to 'squeeze' IS -

South of Aleppo city, Al-Nusra Front and allied jihadists late Monday seized a set of strategic hilltops held by pro-regime forces at Al-Eis, detonating five car bombs during their offensive, the Observatory said.

"Fighters from Al-Nusra Front, Jund Al-Aqsa, and other groups seized the central Al-Eis hilltop and surrounding hills as well," Abdel Rahman told AFP.

"The hilltops are important because they reinforce the regime's presence in the outskirts of Aleppo and gave them a presence near the main highway south towards Damascus," he said.

A plan agreed by world powers last year calls for a ceasefire, the creation of a transitional body, the drafting of a new constitution and fresh elections.

The main sticking point has been the fate of Assad, whom the opposition insists must step down for any transition to work.

The HNC's Hijab said that if it attends, the issue of a "transitional governing body with no role for Assad" would top its agenda.

Beginning a Middle East visit, US Vice President Joe Biden admitted that finding a political solution would be difficult but there was no other choice.

"So as hard as it is, we have to keep trying to reach a political settlement," he told Abu Dhabi newspaper The National.