A leading Syrian opposition group slammed international talks on Saturday in Lausanne aimed at ending the five-year war, as warplanes pressed fierce raids on second city Aleppo.

Abdal Ahad Stefo, deputy head of the Istanbul-based National Coalition opposition body, told AFP the talks "will only lead to wasting more time, further procrastination, and the shedding of more Syrian blood".

Key global players, including the top diplomats from Russia and the United States, will meet in Switzerland on Saturday for last-ditch talks aimed at ending Syria's five-year war.

UN special envoy Staffan de Mistura, Iran's chief diplomat Mohammad Javad Zarif, and foreign ministers from rebel-backing countries like Qatar are also expected to attend.

But Stefo said the meeting would fail to make any progress as no Syrians were invited.

"The absence of Syrians from these preparatory meetings is one of the problems that has complicated and confused (the path to) a political solution," he said.

"The common denominator among all the meetings that have been held since 2012... until now is the absence of Syrians and a monopolisation by the United States and Russia," Stefo said.

The US and Russia back opposing sides of Syria's conflict but have spearheaded efforts this year to secure a truce and a political settlement to the war.

Two ceasefire deals brokered by the world powers in February and mid-September both collapsed.

"Since February, we've been talking about a truce that would bring a cessation of hostilities, but what happened on the ground was the exact opposite -- more people are besieged and increasingly starving," Stefo said.

"The United States and Russia are the main ones responsible."

More than 800,000 people are living under siege in Syria, with an estimated 250,000 of them encircled by government forces in the eastern half of Aleppo.

Fierce air raids pounded several opposition-held districts of the city on Saturday, according to the Syrian Observatory for Human Rights.

The Britain-based monitoring group did not have immediate word on casualties.

Clashes were raging on the southern and northern edges of Aleppo, as well as in the central district of its Old City, the Observatory said.

Iraq Kurdish leader says time for Mosul battle to begin
Arbil, Iraq (AFP) Oct 15, 2016 - Iraqi Kurdish leader Massud Barzani said Saturday that preparations for the operation to retake Mosul from jihadists have been completed and it is time for the battle to begin.

Forces from Iraq's autonomous Kurdish region are expected to play a major role in the battle for Mosul, the country's second city, which has been held by the Islamic State group since June 2014.

"The time has come to begin the liberation of Mosul," a post on Barzani's official Twitter account said.

"All preparations for the battle to liberate Mosul have been completed," he said in a statement on the Kurdish regional presidency's website.

The launch of the operation is expected to be announced soon, but it will mark only the start of a battle that is likely to be the most difficult and complex yet in the war against IS.

Once the battle is announced, a coalition of heterogenous and sometimes rival Iraqi forces will have to fight their way through IS defences to reach the city, in some cases over distances of dozens of kilometres (miles).

Then they will likely seek to surround the city before launching an assault, marking the start of deadly street fighting with die-hard jihadists in a city with a large civilian population.

The battle may spark a humanitarian crisis, with the United Nations warning that up to one million people may be displaced by the fighting as winter sets in.