Tens of thousands of Syrian protesters took to the streets for anti-government rallies, activists said, as regime forces pounded rebel cities, earning a stern rebuke from UN chief Ban Ki-moon.
At least 35 people were killed on Friday, 22 of them civilians, the Britain-based Syrian Observatory for Human Rights said -- suggesting Damascus's pledge to immediately withdraw forces from protest hubs had gone unfulfilled.
Ban said attacks by government forces violated a UN Security Council demand for an end to hostilities, and urged Syrian President Bashar al-Assad not to use an April 10 peace plan deadline as an "excuse" for more killing.
UN-Arab League envoy Kofi Annan has warned of "alarming" casualties as the government's year-long crackdown on dissent -- which the UN says has left more than 9,000 dead -- showed no signs of abating.
Fresh anti-regime rallies were held Friday in Kurdish areas of northern Syria, in the eastern province of Deir Ezzor, and in Idlib province, which lies on the border with Turkey, said Rami Abdel Rahman, head of the Observatory.
An activist on the ground, Dib al-Dimashki, told AFP in Beirut by telephone that marches were also held in several districts of Damascus.
Large demonstrations were also reported in southern Daraa province, cradle of the revolt.
On its Facebook page, the Syrian Revolution 2011 activist group had urged Syrians to demonstrate in favour of arming anti-regime rebels.
The Local Coordination Committees group said security forces shot at demonstrators in Douma, north of Damascus, in the central city of Hama and in Idlib.
Of the 35 people killed on Friday, 11 died in the flashpoint central province of Homs and the same number in the Aleppo region in the country's north, the Observatory said.
Aside from the 22 civilian fatalities, nine soldiers and four deserters also lost their lives.
The Observatory reported fierce battles in the villages of Al-Tiba, Al-Qabu and Shniyeh in Homs province. The clashes erupted after loyalist militias opened fire on seven women, killing two and wounding four.
It said regime forces were pounding districts of Homs city and Rastan to the north, with searches under way in the Damascus suburbs after a night of clashes with deserters in which three soldiers were killed.
Ban denounced the latest violence, in comments conveyed by his spokesman Martin Nesirky.
The UN chief "deplores the assault by the Syrian authorities against innocent civilians... despite the commitments by the government of Syria to cease all use of heavy weapons in population centres," said Nesirky.
"The April 10 timeline to fulfil the government's implementation of its commitments, as endorsed by the Security Council, is not an excuse for continued killing," Ban added.
"Such actions violate the consensus position of the Security Council" which backed the six-point peace plan drawn up by Annan and the deadline he agreed with Assad, he said, according to Nesirky.
The Security Council passed one statement backing Annan's peace plan and on Thursday agreed a second "presidential statement" formally endorsing the April 10 limit for Syrian troops and big guns to be pulled out of cities.
Russia and China, which blocked two Council resolutions on Syria, have signed up to the new demands.
Ban said he was "gravely concerned" at the worsening humanitarian crisis in Syria, adding that the growing number of refugees pouring over the border into neighbouring countries was "alarming."
Ankara urged the United Nations and international community to reinforce efforts to aid Syrian refugees after a record 2,800 people poured across the border in less than two days, taking the number in Turkey to nearly 24,000.
"The Syrian authorities remain fully accountable for grave violations of human rights and international humanitarian law. These must stop at once," the UN leader said.
Ban "demands that the government of Syria immediately and unconditionally cease all military actions against the Syrian people," his spokesman added.
But Syria said on Friday that the number of what it calls "terrorist acts" had risen since the deal was reached with Annan.
"The terrorist acts committed by the armed terrorist groups in Syria have increased during the last few days, particularly after reaching an understanding on Kofi Annan's plan," it said in a letter to Ban.
At the same time, Damascus lashed out at the UN high commissioner for human rights, accusing her of turning a blind eye to "terrorism" funded from abroad.
Damascus has also demanded a written commitment that the opposition will not seek to exploit the troop withdrawal to make territorial gains.
A UN advance team headed by a Norwegian general had arrived in Syria to discuss the eventual deployment of a UN supervising mission, Annan's spokesman said on Thursday.
The United Nations says more than 9,000 people have been killed in the regime's crackdown on the year-old uprising. Activists say more than 10,000 people have died.