Aid teams are standing ready to enter the contested Syrian city of Homs to evacuate people trapped and wounded by 10 days of fighting between rebels and forces loyal to President Bashar al-Assad.
Both sides had agreed to a temporary truce, the International Committee of the Red Cross (ICRC) said from Geneva.
Teams from the ICRC and its partner, the Syrian Red Crescent, were ready to go into Homs as soon as possible, pending final arrangements.
Khaled Erksoussi, head of the Red Crescent's emergency operations, said Syrian authorities approved the operation, which was supposed to begin later on Thursday.
Rabab al-Rifai, an ICRC spokesperson, said aid groups would distribute humanitarian goods such as medical kits in the neighborhoods that have endured shelling and clashes.
"Fighting has been raging for more than 10 days between the Syrian army and armed opposition groups in several
neighbourhoods of Homs city," Beatrice Megevand-Roggo, the ICRC's regional head of operations, said.
"Hundreds of civilians are stuck in the old city of Homs, unable to leave and find refuge in safer areas, because of the ongoing armed confrontations."
Activists said shelling in the district of Khalidiya in Homs continued on Thursday. Witnesses said the Syrian army had also been using helicopters to target some areas of the city.
Pro-opposition Homs residents said rebels and troops were still locked in fierce battles on Wednesday evening in the
neighbourhoods the ICRC wanted to enter.
"They are still firing mortars and missiles into the city and there is heavy fighting in al-Qusour, al-Qarabis and
al-Khalidiya," Abu Yazen, an activist, said.
Homs has been at the centre of the 15-month revolt against Assad and became the focus of world concern in February and March, when opposition-held neighbourhoods endured weeks of government bombardments and sniper fire in which hundreds of people were killed.
A Homs resident said a similar evacuation agreement was reached a few days ago but collapsed when shots were fired by Assad's forces.
The government said on Tuesday it was trying to evacuate civilians and blamed rebel fighters for obstructing efforts to get people out safely.
In other action, rebels stormed an army barracks in the northwestern province of Latakia overnight and killed at least
20 soldiers, the pro-opposition Syrian Observatory for Human Rights (SOHR) said.
The rebels had captured some soldiers, including a colonel, and seized machine guns and rocket-propelled grenades, it said. Latakia, a Mediterranean coastal province and home to Syria's main port, was relatively free of warfare until the past month.
It was not possible to verify independently the reports because of tight Syrian restrictions on media access.
World leaders disagree
As the action unfolded in Syria, world leaders aired their differences over the conflict at the G20 Summit at the Mexican resort of Los Cabos.
US President Barack Obama said Assad, whose family has ruled Syria for four decades, had lost all legitimacy and that it was impossible to conceive of any solution to the violence that left him in power.
But Russian President Vladimir Putin said at the end of the summit: "We believe that nobody has the right to
decide for other nations who should be brought to power, who should be removed from power."
Alarmed but apparently impotent to resolve the crisis, the outside world is deeply divided in its response to the
increasingly sectarian conflict that threatens to become a proxy war for regional powers.
Western nations and their Sunni Muslim allies in the Gulf and Turkey seek Assad's overthrow but are wary of intervention, while Russia, China and Iran - Assad's strategic ally - have protected Assad from a tough international response.
The UN says more than 10,000 people have been killed by government forces during the conflict, while Syria
says at least 2,600 members of the military and security forces have been killed by what it calls foreign-backed "Islamist terrorists".
International efforts to halt the violence are deadlocked because Russia and China, which hold veto power in the UN
Security Council, have blocked tougher action against Assad.
They say the solution must come through political dialogue, an approach most of the Syrian opposition rejects.
But a peace plan proposed by international envoy Kofi Annan has all but collapsed and the West is unwilling to intervene militarily, as it did in Libya last year to seal the fate of Muammar Gaddafi.
The situation has now become so dire that a UN observer force, orginally deployed to monitor a ceasefire,
halted patrols on Saturday after convoys were shot at and attacked by crowds.
Rami Abdelrahman, SOHR head, said that in the Latakia barracks raid, fighting went on from Tuesday late until just
before dawn on Wednesday. Two buildings were destroyed, he said.
In-depth coverage of escalating violence across Syria
In assaults against opposition strongholds across the country, soldiers and militias loyal to Assad killed 19 people
on Wednesday, he said.
Six fatalities were on the outskirts of Damascus, which the government has shelled in an attempt to claw back ground lost to the rebels who had set up their own checkpoints.
Activists in central Hama city said the army shelled Arbaeen neighbourhood and troops were preparing to the storm the area.
Also on Wednesday, a convoy carrying an Italian journalist was hit by two roadside bombs, killing a Syrian policeman and wounding three others, while it was travelling to the southern town of Deraa, the Italian news agency ANSA said.
Claudio Accogli, an ANSA correspondent, was unhurt.
What began as a peaceful protest movement has developed into a civil war between the armed factions, marked by a campaign of repression by Assad's forces that has been internationally condemned for its ferocity.
Despite Western diplomatic and moral support for the rebels, the large, well-equipped government forces have them outgunned, making a swift resolution to the conflict an unlikely prospect.