GENEVA, Nov. 29 (Xinhua) -- The outgoing UN special adviser on humanitarian affairs for Syria Jan Egeland warned here on Thursday of a worsening war situation around western Aleppo and Idlib in Syria, saying it is "serious".

"We are very worried about recent developments," he said when giving his final press conference after serving for three years as head of a 23-nation task force for UN Special Envoy for Syria Staffan de Mistura.

Describing the situation as akin to a "giant powder keg", Egeland said: "Over recent days we have seen provocations and counter-provocations, exchanges of mortars and grenades."

"We have seen increasing incursions in both directions," he noted, saying "This is the worst possible kind of action in the worst possible place."

"We allowed all hell to be let loose in the most heavily populated of civilian places ...and no one was willing and able to shield and protect them. I happen to believe that what happened here in Geneva helped cause some of the few really achievements, also in the protection of civilians," he said.

During his meeting Thursday with De Mistura, the UN adviser has led the push to reach besieged and vulnerable civilians in Syria afflicted by the seven-year-long war and "congratulated Russia and Turkey" for committing to keep a buffer zone around Idlib.

Idlib has emerged as the major destination and stronghold for the Syrian rebels fleeing other parts of the country after deals or surrender.

In recent months, the Syrian army captured several towns in the southern countryside of Idlib, with hundreds of people starting to return to those areas.

The major rebel group in Idlib is the Levent Liberation Committee, otherwise known as the al-Qaida-linked Nusra Front.

Idlib lies close to the international road linking the capital Damascus with the northern province of Aleppo and is home to around 2.5 million people, including those evacuated after the surrender of rebels in other Syrian areas.

Egeland spoke after De Mistura had issued a statement here Thursday saying that a meeting he attended in the Kazakhstan capital of Astana involving Russian, Iranian and Turkish diplomats ended with "no tangible progress."

It was seeking to overcome a ten-month stalemate on the composition of the constitutional committee as outlined in the Sochi Final Statement of Jan. 30 in line with the 2015 UN Security Council resolution 2254 on Syria.

De Mistura, who was appointed in July 2015, is also stepping down as the UN Special Envoy on Syria after being the longest serving person in the post following his predecessor Kofi Annan and Lakhdar Brahimi.