Syria's army Wednesday launched a fierce assault against rebels in the Damascus region, shelling neighbourhoods and sealing main entrances to the capital, witnesses said, as prospects for peace talks dimmed.
In other violence, two suicide car bombings killed at least 19 members of the security forces in attacks targeting a military intelligence headquarters in the south-central city of Palmyra, said the Syrian Observatory for Human Rights.
The fighting came as a proposal by opposition leader Ahmed Moaz al-Khatib for peace talks with President Bashar al-Assad's regime suffered sharp setbacks, with Damascus ignoring it and a key opposing faction flatly rejecting the initiative.
The surprise gesture by Khatib, head of the opposition National Coalition, has been welcomed by Washington and the Arab League and was expected to receive the support of the Organisation of Islamic Cooperation (OIC) summit in Cairo later Wednesday.
Assad himself has yet to comment on the offer by Khatib, who says "the ball is now in the regime's court", but the pro-regime Al-Watan newspaper said the offer came two years too late.
The Syrian National Council, the main component of the Coalition, rejected the possibility of any talks, saying it was committed to ousting Assad's regime, rejecting dialogue with it, and protecting the revolution.
Addressing the OIC summit, Egyptian President Mohamed Morsi alluded to the splits in the ranks of the opposition laid bare by Khatib's unexpected announcement, calling on opposition parties "to coordinate with this coalition and support their efforts for a unified approach... for democracy".
According to a draft OIC resolution obtained by AFP, the summit is to call for "serious dialogue" between the Syrian opposition and government officials "not directly involved in oppression".
The document stresses the need to maintain "Syria's territorial integrity and sovereignty", while underlining that "the main responsibility for the continued violence falls on the Syrian government".
Khatib's offer on Monday followed his surprise announcement last week that he was ready for talks with the regime, subject to conditions including the release of 160,000 detainees.
Khatib later elaborated, saying he was ready to meet Syrian Vice President Faruq al-Sharaa.
In the past the opposition has demanded President Assad step down before talks can begin but analysts say Khatib's change in stance stems from a belief the population will be bled dry while the West fails to act.
Assad's regime on Wednesday signalled it believes it can still break the military stalemate that has seen his forces and rebels more or less hold their ground in the past few months, relentlessly pounding rebel lines around Damascus.
"The province was bombed very badly, in attacks that have not been seen in months. There was also very heavy fighting," said Rami Abdel Rahman, the director of the Britain-based Observatory.
A Syrian security official in Damascus who declined to be named said that "the army has launched a coordinated all-out offensive on all of the areas surrounding the capital.
"All entries to Damascus have been sealed," he added.
Local residents said that "unusually intense bombing" was heard throughout the capital all day on Wednesday.
In the south-central city of Palmyra, two suicide car bombings targeting a military intelligence headquarters killed 19 members of the security forces, the Observatory said.
The deaths added to an initial toll by the watchdog of 69 people -- 30 civilians, 22 troops and 17 rebels -- killed nationwide on Wednesday.
The United Nations says more than 60,000 people have been killed since the start of an uprising against the Assad regime in March 2011.