Latest reports from Syria say government forces have resumed their bombardment of the city of Homs, as Russia's foreign minister is due to arrive in Damascus for talks.
Hundreds of people are reported to have been killed since government troops began pounding opposition strongholds in the city - a centre of resistance to the regime of President Bashar al-Assad.
A BBC correspondent who has managed to enter Homs says residents fear Syrian troops are planning to launch a ground assault on the city after unconfirmed reports said troops had moved within 1km of parts of the city under bombardment.
He says the new shelling began at 6am and he describes it as fairly heavy fire.
Syrian forces began an incessant bombardment of the city at 6am on Monday and kept the pressure up for most of the day.
Intermittent shelling continued during the night and residents burying their dead in mass graves under the cover of darkness came under fire.
The government says its forces are fighting armed gangs and terrorists.
Russian foreign minister Sergei Lavrov is expected in Syria on Tuesday for talks with President Bashar Al-Assad.
His visit comes amidst western anger that Russia, along with China, used its veto powers to block a UN Security Council resolution that backed an Arab League peace plan for Syria.
Mr Lavrov said Western reaction to Moscow's veto had bordered on hysteria.
His office said he was heading to Damascus because Moscow sought the swiftest stabilisation of the situation in Syria.
Meanwhile, US President Barack Obama says he believes time is running out for the government of President Assad.
Mr Obama says he senses more and more people inside Syria recognising that they need to turn a chapter and the Assad regime feeling the noose tightening around them.
This is not going to be a matter of if, it's going to be a matter of when.
Earlier, the US closed its embassy in Syria and pulled its diplomats out of the country in response to the worsening security situation there.
Britain has also recalled its ambassador from Syria.