BEIRUT (AFP) - World leaders hailed "real progress" in Syria on Friday (March 4), but fresh air strikes showed the fragility of the week-old truce and the many obstacles still in the way of peace talks.

Warplanes struck a key rebel bastion east of the Syrian capital for the first time since the fragile truce began last weekend, a monitor said.

"Two air strikes hit the edge of the town of Douma in Eastern Ghouta and one person was killed," said Rami Abdel Rahman, head of the Britain-based Syrian Observatory for Human Rights.

He said the strikes were conducted by either Syrian or Russian planes.

Eastern Ghouta, the largest rebel bastion east of Damascus, was regularly and fiercely bombarded by government forces, but has been relatively calm since the ceasefire brokered by the United States and Russia.

"This cessation of hostilities is by no means perfect but it has reduced the level of violence, it has created an opportunity for some humanitarian access," said British Foreign Secretary Philip Hammond after meeting with his French, German and EU counterparts in Paris.

The group said the focus now was on convincing all parties to return to UN-brokered peace talks in Switzerland.

"We want a speedy resumption of the negotiations in Geneva, but two conditions must be fulfilled: access for all Syrians to humanitarian aid, and full respect of the ceasefire," said French Foreign Minister Jean-Marc Ayrault.

The group also met with Riad Hijab, head of Syria's main opposition body, the High Negotiations Committee which has expressed scepticism that the regime will stick to the truce.

"We've encouraged Dr Hijab, whatever his reservations, to be prepared to return to the discussions in Geneva," said Hammond.

For the first time in years, hundreds of Syrians nationwide took advantage of the truce to resume anti-government protests under the slogan "The Revolution Continues!" Waving the three-starred tricolour flag that has become the uprising's emblem, demonstrators in opposition-held areas of Aleppo, Damascus, Daraa and Homs called for the downfall of President Bashar al-Assad's regime.

"You could say we've gone back to the beginning," said Hasaan Abu Nuh, an activist from the flashpoint rebel town of Talbisseh in central Homs province.

Meanwhile, world leaders expressed a sharp difference of opinion over Assad's plans to hold elections next month - way ahead of a roadmap agreed in November that did not envision polls for at least 18 months.

"The idea that there could be elections (in April) is not just provocative but totally unrealistic," said French President Francois Hollande, after meeting his German counterpart Angela Merkel in Paris.

But Assad's key ally, Russian President Vladimir Putin, shot back that the plan for elections "does not interfere with steps to build the peace process".

Doctors Without Borders (MSF) said tens of thousands of displaced Syrians along Turkey's border have not returned home despite the truce.

"Some 100,000 people gathered near the border - including 50,000 in past weeks after the spike in violence in early February from the Syrian government coalition - have not yet started to return home because it's too dangerous," MSF head Joanne Liu told AFP.

"We're in a transition period and I think it will take another few days for things to settle and for people to become convinced there really is a truce."

But "the movement of people fleeing the (northern) Idlib and Aleppo provinces to the border has decreased enormously", she added.

An official in the UN's humanitarian coordination office told AFP that a convoy of "food, nutrition, and medical supplies" was to be distributed to 20,000 people in the rebel bastion of Eastern Ghouta.

The Syrian opposition has criticised both the regime and the United Nations for what it says are delayed and insufficient deliveries.

Hijab said Thursday that aid was "only entering very limited areas".