A Russian-negotiated ceasefire has gone into effect in Syria's Eastern Ghouta, the last remaining rebel stronghold near the capital, Damascus.

The truce, which started Saturday, is expected to bring temporary relief to an estimated 400,000 people in the area suffering from acute food and medicine shortages.

Eastern Ghouta has been under a government siege since 2013.

Al Jazeera's Stefanie Dekker, reporting near the Turkish-Syrian border, said Eastern Ghouta's proximity to Damascus underlines the importance of the area to the government of Bashar al-Assad.

It is reported that the region "has the worst cases of malnutrition in the entirety of the Syrian war", our correspondent said.

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The ceasefire was negotiated in Vienna.

Not all opposition factions in Eastern Ghouta signed up to the deal, and it remains to be seen how long it will hold, our correspondent said.

"The proof is to see the developments on the ground. I think we have to wait and see how it turns out," she said.

Over the past two months, Russian jets and the Syrian army have intensified their bombardment of the rebel enclave.

Sochi talks

News of the deal comes as the Syrian opposition announced it plans to boycott Russia-hosted peace talks in Sochi next week, saying it is an attempt to undercut the United Nations' effort to broker a deal.

Saturday's announcement was made in in Vienna, where the latest round of UN talks between Syria's government and the opposition wrapped without major breakthroughs.

"We listened to many guarantees concerning commitment, but none of them were delivered somehow," said Yahya al-Aridi, Syrian opposition spokesman, following the announcement.

"We are tired of that, we need real involvement, we need real commitment," he told Al Jazeera.

Aridi said it was up to Russia to put more pressure on the Syrian government to make concrete steps to resolve the crisis, which is now in its seventh year.

"We believe that the ball is in the Russian court," he said. "They say that they have the upper hand in Syria and they were responsible for saving this regime for a long time, and they can bring it to commit itself to international legality resolutions and if they want, they can."

In a separate press conference on Saturday morning, Nasr al-Hariri, leader of the Syrian opposition delegation, also called on the Assad regime to commit to "tangible goals" set by the UN.

So far, nine rounds of UN talks between the warring sides have made little progress towards ending the civil war.

'No to foreign interference'

Staffan de Mistura, the UN special envoy for Syria, said he has not decided whether he will attend the talks in Russia.

Mistura said he shared the frustration of millions of Syrians at the lack of a political settlement to date.

"Ultimately, what is required is political will," he said. "It is high time that diplomacy, dialogue and negotiations prevail for the interest of all Syrians."

Earlier, Saudi Arabia, Jordan, US, Britain and France submitted a document to Mistura recommending a "practical approach" to achieve peace, including reforming the Syrian constitution and the conduct of "free and fair elections".

Bashar al-Jaafari, Syria's chief negotiator and representative to the UN, said the document was "unacceptable".

"Our people have not and will never accept a solution that is parachuted onto them or that is carried on tanks," he said in a statement to reporters.

"The goal of the conference in Sochi is to engage in a national intra-Syrian dialogue without foreign interference. The conference will be attended by about 1,600 participants who will reflect the various components of Syrian society," he added.

With the retreat of the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) in Syria, Assad's forces have regained several territories, while putting the opposition on the defensive.

Elsewhere, in Syria's northern Kurdish enclave of Afrin, Turkish forces and the Free Syrian Army (FSA) continue their march into the city as they continue their operation against the US-backed Kurdish armed group YPG.

The fighting has complicated relations between Turkey and the US, which are both opposed to the Syrian regime, but have found itself in the opposite sides against the Kurds.

As of Saturday morning, there have been at least 394 YPG fighters killed since the beginning of the operation, the Turkish military said.

"We are fighting the YPG because they betrayed us, and especially because they took over my city, Tal Rifaat," Mohammed Abu Ahmed, an FSA fighter battling alongside the Turkish troops, told Al Jazeera.

"I have been displaced along with many of my neighbours for two years living in the camps," he said. "There are such bad conditions especially now in the winter."

In Afrin's neighbouring Syrian city of Azaz, which is controlled by the FSA after the group retook the area from ISIL in 2014, life remains difficult in the predominantly Sunni area.

Nazha Hilal, a shopkeeper and Azaz resident, told Al Jazeera that she is all alone in providing food for 13 members of her family.

"People like us are used to the shelling and the explosions," Hilal told Al Jazeera. "The young children are still scared, but we've been facing this for a few years now. We're not afraid any more."

Syria's conflict, which started with peaceful anti-government demonstrations in March 2011, escalated into a full-blown war that has claimed more than 400,000 lives and driven about half of the country's prewar population of 22 million from their homes.