Syria: Fierce clashes in provincial capital Raqqa
Ferocious fighting has erupted around the northern provincial capital of Raqqa in Syria - one of several clashes between government and rebels forces.
Government forces shelled several areas of the city, while running battles on the outskirts of the city since dawn had left dozens dead, activists said.
Fighting also raged at a police academy near Aleppo, in the rebel enclave of Daraya and around Damascus.
The violence comes amid fresh diplomacy aimed at ending the ongoing conflict.
The crisis in Syria has been a central issue in John Kerry's first overseas trip as US secretary of state.
Visiting the Turkish capital on Friday, he said the US and Turkey believed "the first priority is to try and have a political solution. We would like to save lives, not see them caught up in a continuing war".
UN Secretary General Ban Ki Moon said he was "personally pained and distraught" by the ongoing violence and suffering of civilians, adding that there was a "very small window of opportunity" for the Syrian government and the opposition to hold talks.
But the BBC's Jim Muir, monitoring the conflict from Beirut, says that despite the huge amount of diplomacy going on, there is little actual movement.
There is a war going on all over the country, a slow steady grind on the ground, our correspondent adds.'Dozens dead'
"Fierce clashes pitting rebel fighters from several battalions against regular troops have raged since dawn" on the outskirts of Raqqa city, the British based Syrian Observatory for Human Rights (SOHR) said.
"Army troops shelled several city neighbourhoods, as well as the outskirts, while the clashes left dozens of troops and rebels dead," the group added, although the casualty figures cannot be independently verified.
Raqqa city is near Syria's northern border with Turkey and residents say it has become home to thousands of people forced to flee their homes in other war-torn parts of Syria.
Meanwhile, video was published appearing to show insurgents storming the main police academy building of the Khan al-Assal complex outside Aleppo.
The footage showed several dozen fighters running to the complex and sheltering by an outer wall amid the sound of rapid gunfire and the sight of explosions within the grounds of the academy.
Earlier, on Friday, Syrian troops retook a checkpoint on the north-eastern border with Lebanon at Yaarubiyeh, captured a day earlier by Islamist fighters, reports said.
Fresh battles on Saturday also shook Daraya, southwest of Damascus which the army has being fighting to take back from insurgents for weeks, the SOHR said.
The nearby rebel-held town of Moadamiyat al-Sham also came under government bombardment and there was fighting in Douma, north-east of Damascus.
Also on Saturday, Syria and Iran accused the US of double standards over its decision to provide aid to rebels fighting to topple President Bashar Assad and said the move would only prolong the conflict.
The remarks from the nations' foreign ministers came after Mr Kerry announced this week that Washington will provide non-lethal aid - like food and medical supplies - directly to Syria's rebels, in addition to $60m in aid to Syria's political opposition.