Residents in the Syrian city of Homs say they have seen the most intense bombardment so far, in five days of shelling.
Tanks are on the streets and there are unconfirmed reports that pro-government militias are killing civilians in their homes.
A BBC correspondent on the outskirts of Homs on Wednesday said the city is full of rumours and most people are too terrified to venture outside.
President Bashar al-Assad promised Russian foreign minister Sergei Lavrov in Damascus on Tuesday that he would end the violence and start dialogue.
Russia and China blocked a UN Security Council resolution last week.
Prime Minister Vladimir Putin of Russia has warned against outside intervention in Syria, saying one cannot act like a bull in a china shop.
The Syrian government blames the violence on foreign-backed groups and insisted the offensive in Homs would continue until "order" is restored in the city.
Meanwhile, Turkey is preparing new diplomatic moves to put pressure on Syria's President Bashar al-Assad to stop the fighting.
Foreign minister Ahmet Davutoglu says that if the United Nations Security Council fails to protect civilians, then like-minded countries should find ways to end the killing and help civilians.
Robert Fisk, Middle East correspondent for the Independent newspaper, is observing the situation from neighbouring Beruit.
He told Morning Report that Syria has powerful neighbours and Mr Assad will remain in office for quite a long time yet.