The Syrian opposition says UN observers have failed to end the violence in the country and are calling for the creation of "safe zones" to allow humanitarian aid to get through.
Radwan Ziadeh, director of foreign relations at the Syrian National Council, told Al Jazeera the UN was naive to believe the Syrian government would comply with its peace plan.
"The only language [President Bashar] al-Assad's regime will understand is using force against him," he said.
"That is why it is important now to tackle the humanitarian disaster by implementing the safe zone and having no fly zones.
"Sending observers and all of that will not enforce Assad to stop the killings."
His comments come as further violence was reported on Sunday in the central flashpoint city of Homs, as UN observers toured an embattled neighbourhood within the area.
Gun battles still frequently erupt in Syria's third largest city, which has emerged as the heart of the uprising.
Al Jazeera is unable to independently verify reports of violence, as the Syrian government has placed strict restrictions on foreign media in the country.
'Salvage peace plan'
The Syrian state news agency said the observers toured the Khaldiyeh district of Homs, which has seen heavy government shelling and clashes between government forces and opposition fighters.
The team in Homs is part of an advance team of 15 UN monitors in Syria who are trying to salvage a peace plan brokered by special envoy Kofi Annan that aims to end the country's 13-month-old crisis.
Under the plan, a ceasefire is supposed to lead to talks between Assad and the opposition on a political solution to the conflict that the UN estimates has killed more than 9,000 people. The government says 2,500 members of the security forces have been killed.
But the plan has been deeply troubled since the truce began on April 12. The Syrian government has kept up its attacks on opposition strongholds, while opposition fighters continue to ambush security forces.
Defying a major truce provision, the Syrian military has failed to withdraw tanks and soldiers from the streets.
Most analysts say the plan has little chance of succeeding, though it could temporarily bring down the level of daily violence.
Meanwhile, the Lebanese navy intercepted a ship loaded with three containers of weapons reportedly destined for Syrian opposition forces on Saturday.
Pictures released by the army showed dozens of crates inside the containers, some of them filled with belts of heavy ammunition and rocket-propelled grenades.
Military prosecutor Saqr Saqr said an investigation was under way, adding that the 11 crew members of the cargo vessel, which originated from Libya, were being questioned by Lebanese military police.
|Lebanon says weapons seized on the Sierra Leone-registered ship were bound for the opposition
A security official said the Sierre Leone-flagged Lutfallah II was bound for members of the Free Syrian Army, an umbrella group of fighters trying to overthrow Assad's government.
Syrian authorities have repeatedly charged that weapons are being smuggled from Lebanon to groups fighting to overthrow Assad.
UN chief Ban Ki-moon has blamed the Syrian government for widespread ceasefire violations, prompting Syria to respond that his comments were "outrageous'' and accusing him of bias.
Ban and Annan have cited violations by both sides, but generally portrayed the Syrian government as the main aggressor.
Under the peace plan, the UN is to deploy as many as 300 truce monitors.
One hundred should be in the country by mid-May, and Norwegian Major General Robert Mood, the head of the observer team, arrived in Damascus on Sunday to assume command.