Foreign experts will visit protest cities, while UN chief condemns Syrian leader for past year of "brutal repression".
The United Nations has said it will send experts on a Syrian government-led humanitarian mission, while the world body's leader Ban Ki-moon strongly condemned the past year of "brutal repression" by President Bashar al-Assad.
Valerie Amos, the UN humanitarian chief, said on Thursday that UN technical experts would be joining a Syrian "government-led" mission and again demanded free access to protest cities.
Analysts said the Damascus mission, which will go to the protest cities of Homs, Deraa and Hama where thousands have been killed, falls short of an earlier offer of a joint assessment mission.
Amos said the mission would start this weekend and would also go to Tartous, Lattakia, Aleppo, Deir al-Zor and rural areas around Damascus.
She said technical staff from the UN and Organisation of Islamic Cooperation would join the mission "and take the opportunity to gather information on the overall humanitarian situation and observe first-hand the conditions in various towns and cities".
But Amos stressed that "it is increasingly vital that humanitarian organisations have unhindered access to identify urgent needs and provide emergency care and basic supplies. There is no time to waste".
In a message to mark the first anniversary of the start of protests in Syria, Ban said Assad has "responded with brutal repression, which has continued unabated.
"Its consequences are tragically unfolding before the world's eyes. Well over 8,000 are dead as a result of the government's decision to choose violent repression over peaceful political dialogue and genuine change," Ban said.
"It is urgent to break the cycle of violence, stop military operations against civilians and prevent a further militarisation of the conflict in Syria. The status quo in Syria is indefensible."
Ban expressed "solidarity" with the Syrian people and called on the Syrian government and opposition to co-operate with UN-Arab League envoy Kofi Annan, who will brief the UN Security Council on Friday.
The UN chief added that he "appeals to the international community to offer its determined and unified support to stop the bloodshed and find a political solution that responds to the will of the Syrian people and ensure respect for their fundamental rights".
As the opposition marked the first anniversary of the revolt on Thursday, government troops pressed ahead with their efforts to control key cities in the south and north.
In Idlib in the north, soldiers have driven out rebel forces and many civilians, and in Deraa, the site of the country's first major anti-government protests in March 2011, soldiers supported by armoured vehicles have launched renewed attacks.
Assad supporters marked the occasion with rallies across the country, including in the capital Damascus, saying the uprising was a "conspiracy" against the state.
Pro-Assad rallies were also held in Suweida to the south and al-Hassake in the northeast.
"After a whole year of pressure on Syria, we want to make the world hear our voice: Leave Syria in peace," a woman on the street told a government television station.
The most prominent opposition bloc, the Syrian National Council, has said it wants to arm civilians and defected soldiers fighting the vastly better-provisioned army, but most nations who oppose Assad's crackdown also fear intervening militarily.
France's foreign minister, Alain Juppe, said arming the opposition risks pushing the country into a catastrophic civil war.
"The Syrian people are deeply divided, and if we give arms to a certain faction of the Syrian opposition, we would make a civil war among Christians, Alawites, Sunnis and Shias,'' Juppe said on France-Culture radio.
The government's military offensive has forced thousands of Syrians to flee the country, most of them to neighbouring Lebanon and Turkey. The UN's refugee agency says that about 230,000 Syrians have fled their homes, of whom almost 30,000 have left the country.
Turkey is hosting more than 14,000 Syrian refugees, a foreign ministry spokesman said on Thursday, and the tide is increasing. Roughly 1,000 Syrians came over the border in the past 24 hours, he said.