BEIRUT (AFP) - Syria's conflict entered its fifth year on Sunday with the regime emboldened by shifting international attention, and a growing humanitarian crisis exacerbated by the rise of the Islamic State in Iraq and Syria (ISIS) group.

More than 215,000 people have been killed and half of the country's population displaced, prompting human rights groups to accuse the international community of "failing Syria".

The country has been carved up by government forces, extremist groups, Kurdish fighters and the remaining non-extremist rebels.

Diplomacy remains stalled, with two rounds of peace talks achieving no progress and even a proposal for a local ceasefire in second city Aleppo fizzling out.

The conflict began as an anti-government uprising, with protesters taking to the streets on March 15, 2011, inspired by similar revolts in Egypt and Tunisia.

But a fierce government crackdown on the demonstrations prompted a militarisation of the uprising and its descent into today's brutal multi-front conflict.

The consequences have been devastating.

The Syrian Observatory for Human Rights said at least 215,518 people had been killed in four years of conflict, nearly a third of them civilians and including more than 10,000 children.

The full toll is likely to be even higher, because the fate of tens of thousands of missing people remains unknown.

The UN refugee agency UNHCR says Syria is now "the biggest humanitarian emergency of our era".

Around four million people have fled abroad, with more than a million taking refuge in neighbouring Lebanon.

Inside Syria, more than seven million people have been displaced, and the UN says around 60 percent of the population now lives in poverty.

The country's infrastructure has been decimated, its currency is in free fall and economists say the economy has been set back by some 30 years.

ASSAD REGIME EMBOLDENED

Human rights groups have documented horrific abuses.

The Britain-based Observatory said that 13,000 people had been tortured to death in government custody since the uprising began.

Tens of thousands more remain in regime jails and detention facilities, with many effectively disappearing after their arrest.

Despite international outrage at the death toll, and allegations that his regime used chemical weapons against its own people in August 2013, President Bashar al-Assad has clung to power.

His forces have consolidated their grip on the capital Damascus and are moving to encircle rebels in Aleppo to the north.

The assaults have been aided by the government's increasing reliance on crude barrel bombs, which Assad denies using despite extensive documentation.

His government has been emboldened by both its military successes and an apparent shift in international rhetoric.

Calls for his resignation have been notably more muted as international attention shifts to the threat posed by ISIS.

Diplomats describe a new willingness to countenance a role for Assad in Syria's future, and even the rhetoric from key Assad opponent Washington has shifted.

On Friday, CIA director John Brennan said Washington was concerned that the "collapse" of Syria's government could open the way to an Islamist takeover.

And US Secretary of State John Kerry has said Washington's top priority is defeating ISIS.

LITTLE PROSPECT FOR PEACE

Last year, the United States assembled a coalition of nations to fight the group in Syria and Iraq, where the extremists rule a swathe of territory they have deemed an Islamic "caliphate".

Coalition air support has helped Kurdish fighters to roll back some ISIS gains in Syria, but the group continues to wield significant power.

It has grabbed international headlines with gruesome propaganda videos depicting the killings of journalists, aid workers and other civilians.

It has also attracted thousands of foreign fighters, many from the West, prompting concern about the prospect of attacks by returning militants.

Despite the international attention, there is little prospect of a peaceful resolution of the conflict.

Two rounds of UN-sponsored talks in Switzerland failed to achieve progress, and Staffan de Mistura, the third UN envoy to tackle the conflict, has gained little traction with his proposal for a localised ceasefire in Aleppo.

Russia, a key Assad ally, is floating its own dialogue process, and will host talks in Moscow in April, but it remains unclear if the internationally recognised opposition will attend.

On Thursday, a group of 21 human rights groups denounced the international community for failing to implement UN resolutions and end the conflict.

"This is a betrayal of our ideals," said Jan Egeland, secretary general of the Norwegian Refugee Council.