DAMASCUS, Feb. 18 (Xinhua) -- The Syrian army started shelling the rebel positions in Damascus' Eastern Ghouta countryside on Sunday, the pro-government al-Ekhbariah TV reported.

Loud sounds of explosions were heard in the Syrian capital as rebel positions came under attack in Eastern Ghouta, which has returned under the spotlight with a military showdown recently.

The oppositional Syrian Observatory for Human Rights said the Syrian forces fired tens of missiles on Eastern Ghouta, as part of the preparation for a large-scale offensive on that key rebel-held area.

Also, pro-government activists said the Syrian army is paving the way for the offensive with intense shelling targeting the rebel positions in the Bait Sawa, Mesraba, and Nashabiyeh areas in Eastern Ghouta.

The Syrian airstrikes have also targeted tunnels and trenches built by the rebels in southeast of Douma city in that sprawling region.

But a well-informed source in eastern Damascus told Xinhua that the ground battle for Eastern Ghouta had not started yet.

The shelling on Eastern Ghouta came less than 24 hours since the Syrian army brought in massive reinforcements to take part in the offensive to eliminate the rebels' threat in the region.

Earlier in the day, the pro-government al-Watan newspaper reported that marathon negotiations were underway to reach a settlement with the rebels in Eastern Ghouta amid Syrian military buildup on the outskirts of that area in case of the talks fail.

The settlement of the tense situation in Eastern Ghouta was mediated by the Russians, said the paper, adding that the negotiations were called for by the rebels who are under the Syrian military's pressure.

The situation in Eastern Ghouta flared up over the past two months, when the rebels unleashed a massive offensive against a key Syrian military base in the Harasta city in the region.

The exchange of shelling and attacks prompted the UN to send several appeals for reaching a one-month cessation of hostilities to allow for the entry of relief aid to the affected civilians.

However, the situation calmed down over the past three days before the new escalation on Sunday evening.

Syrians in the capital have long been calling for the elimination of the rebels' mortar attacks, which have paralyzed the lives of many residents in the eastern Damascus neighborhoods.

Four key rebel groups are positioned inside Eastern Ghouta, including the Islam Army, Failaq al-Rahman, Ahrar al-Sham and the Levant Liberation Committee, otherwise known as the al-Qaida-linked Nusra Front.