The Red Cross said Monday it was in talks with the Syrian authorities and rebels to halt the violence so that it can deliver aid, amid calls to allow women and children out of the besieged city of Homs.
President Bashar al-Assad, meanwhile, again accused foreigners of funding and arming "terrorist groups" with the aim of destabilising the country, as Iranian warships docked at the port of Tartus in a show of force.
"The International Committee of the Red Cross is exploring several possibilities for delivering urgently needed humanitarian aid," said ICRC spokesman Bijan Farnoudi.
"These include the cessation of fighting in the most affected areas to facilitate swift Syrian Arab Red Crescent and ICRC access to the people in need."
China's influential People's Daily newspaper warned that any Western support for the rebels would trigger a "large-scale civil war."
But in Cairo, top Republican US Senator John McCain called for the opposition to be given weapons to help "defend themselves," while ruling out direct US aid.
"We have seen in Libya, and we have seen in previous conflicts there are ways to get weapons to people so they can defend themselves," McCain said.
US Secretary of State Hillary Clinton, on a visit to Mexico, said for her part that Syria was increasingly under pressure.
She said that an upcoming Friends of Syria meeting, due this week in Tunisia, will "demonstrate that Assad's regime is increasingly isolated and that the brave Syrian people need our support and solidarity."
The meeting "will send a clear message to Russia, China and others who are still unsure about how to handle the increasing violence but are up until now, unfortunately, making the wrong choices," she said.
Despite a weekend appeal by a visiting Chinese envoy in Damascus for the violence to stop, monitors said regime forces targeted the central city of Homs for a 17th straight day.
Attacks there claimed nine of the 16 lives lost across the country on Monday, according to reports by the Syrian Observatory for Human Rights and state media.
Shelling of Baba Amr, the main rebel stronghold in Homs, killed five civilians, while another four died, including three children of the same family, when rockets hit Al-Malaab district, said the Britain-based Observatory.
The official SANA news agency said a lieutenant colonel and a sergeant were killed in a clash with an "armed terrorist group" in Athraya, central Hama province.
Activists say more than 6,000 people activists have died in the Assad regime's 11-month crackdown on dissent.
"Infantry troops arrived yesterday (Sunday) in Homs," Rami Abdel Rahman, head of the Syrian Observatory, told AFP by telephone.
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A Homs-based activist voiced fears of an imminent attack on Baba Amr, speaking of "unprecedented military reinforcements coming from Damascus."
"News has been leaked to us from army officers about a bloody attack that will burn everything in Baba Amr," Hadi Abdullah of the General Commission of the Syrian Revolution said Sunday.
A day after saying Baba Amr was being hit by up to five rockets a minute, Abdullah on Monday demanded safe passage out for women and children.
"We want women and children to be allowed to leave" Baba Amr, he told AFP, adding that "people were suffering from the weather, while their conditions are miserable."
Assad, meeting visiting Russian lawmakers, thanked Moscow for its support, saying that Syria was being "targeted by armed terrorist groups receiving funding and arms from foreign parties aiming to destabilise" it, state media said.
Meanwhile, Tunisia's Foreign Minister Rafik Abdessalem, speaking after a meeting of Mediterranean foreign ministers, said there had been agreement on the need to avoid "an Iraqi scenario" and preserve Syria's integrity.
He also said the Syrian opposition would take part in the "Friends of Syria" conference.
Elsewhere, two warships from Iran, a key backer of Assad's regime, docked at Tartus, Tehran's state television reported, adding that their crew would train Syrian sailors.
And Iraq's interior ministry said its forces had prevented "smugglers and infiltrators" trying to cross from Syria, without saying when this occurred.
In Damascus, regime forces remained on alert after two days of large and unexpected protests, according to activists.
Mohammed Shami, a spokesman for activists in Damascus province, said security was bolstered in some areas in the tense neighbourhood of Mazzeh, including around the Iranian embassy.
Meanwhile, Syrian authorities freed blogger Razan Ghazzawi, symbol of the 11-month uprising, and six other women activists arrested last week, human rights lawyer Anwar Bunni said.
They were part of a group of 14 activists arrested last Thursday in a raid on the Syrian Centre for Media and Freedom of Expression, a group headed by rights activist Mazen Darwish.
Authorities in the northern city of Aleppo also freed film director Firas Fayyad, on trial over charges of spreading false news and belonging to an opposition party, Bunni said.
Secular Syrian groups have called for demonstrations outside parliament in Damascus on Tuesday against the draft constitution being put to a referendum on Sunday.
Article 3 of the draft text, as published by SANA, stipulates that the president be a Muslim and that "Islamic jurisprudence shall be a major source of legislation."