SANA (Syria), CNN (US), REUTERS (UK), AFP ( France)
Reuters reports that UN estimates have almost quadrupled since its last forecast in August reported 185,000 refugees.
The new figures were published as reports circulated that the one-day death toll in Syria reached 343 Wednesday, making it the bloodiest day since the conflict began, reports CNN citing the opposition group Local Coordination Committee in Syria (LCC).
The LCC published the figures of the death count early Thursday morning, citing 162 deaths in Damascus and its surrounding suburbs.
The activist group is also accusing President Bashar al-Assad's forces of carrying out a massacre in al-Dhiyabia, southeast of the capital, where the death toll reached 107.
Rafif Jouejati, a spokesperson for LCC, said: "The staggering numbers are horrific but the world also needs to know that there is increasing sexual torture and more children being tortured.
"The regime is escalating the violence at every possible opportunity and it is proof that it is determined to crush the revolution by any means necessary."
Before the latest report, the deadliest day had been August 25, when the reported death toll reached 330.
The news agency Reuters remained slightly more cautious of the death totals, reporting that more 300 people were killed "in one of the bloodiest days in the 18-month uprising," citing the British based Syrian Observatory for Human Rights as a source.
Fighting has intensified in Syria in the past months, as President Assad mounts pressure on the rebel forces with regular bombardments.
Syrian state-run TV SANA has broadcast CCTV footage of suicide bombings in Damascus Wednesday, targeting the General Staff building.