UN chief Ban Ki-moon Monday urged President Bashar al-Assad to immediately stop the killings of civilians, a day after the Arab League called for "national dialogue" to end violence sweeping Syria.
"There are continuous killings of civilian people. These killings must stop immediately," the UN chief said in Bern.
"I told Assad: 'Stop before it is too late'," said Ban, noting that thousands have perished in the regime's brutal crackdown on dissent.
"It is unacceptable that 3,000 people have been killed. The UN is urging him again to take urgent action," he said.
The UN secretary general also called on Assad to accept an international commission of inquiry into rights violations.
In April, the UN Human Rights Council ordered a probe into the situation in Syria but Damascus blocked investigators from entering the country.
UN human rights chief Navi Pillay said on Friday that more than 3,000 people, including 187 children, have been killed in the fierce crackdown on anti-regime protests that have roiled Syria since mid-March.
Ban's call came as a rights group said five Syrian soldiers were killed during clashes with gunmen suspected to be army defectors in the flashpoint central province of Homs on Monday.
The Syrian Observatory for Human Rights also said two civilians were also killed on Monday, both in the city of Homs itself.
"Five soldiers were killed and others wounded as a result of clashes pitting the army and security forces against gunmen believed to be defectors at a checkpoint near the town of Qurayn in Homs province," the Observatory said in a statement.
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It added that some "20 soldiers fled to the surrounding orchards."
In another confrontation with gunmen thought to be defectors, in the northwestern province of Idlib, "17 in the army's ranks were wounded," the Britain-based watchdog said.
It also reported that Syrian security forces opened fire in the Bab al-Sabaa residential area of Homs, a hotbed of dissent, killing one person and wounding six.
"Another civilian was also shot dead by security forces during a raid in the Al-Khalidiyeh neighbourhood," it added.
In Cairo on Sunday, the Arab League said after an emergency meeting of its foreign ministers that it would make contact with the Damascus government and a raft of oppposition groups with the aim of launching "national dialogue within the seat of the Arab League and under its guidance within 15 days."
Qatari Foreign Minister Sheikh Hamad bin Jassim al-Thani, the chair of the meeting who issued the statement, had insisted the gathering was not convened "under any agenda but to show concern for Syria and the Syrian people. Your brothers want to help."
Gulf states requested the meeting to discuss "the situation in Syria, which has deteriorated sharply, particularly in its humanitarian dimensions, and steps that could help end the bloodshed and halt the machine of violence."
Assad's regime blames "armed gangs" for the violence that has wracked Syria for the past seven months, but activists say most of the deaths are caused by security forces putting down non-violent protests.
The Local Coordination Committees, an activist network spurring protests, meanwhile accused Syrian security forces of intensifying their crackdown on doctors who treat wounded demonstrators.
"Security forces recently intensified their campaign against doctors, hospitals and private clinics suspected of treating people wounded in pro-freedom rallies" without notifying security services, the LCC said in a statement on Monday.
The group said attending physicians are required to immediately notify security services of the arrival of a wounded person, regardless of the severity of his injuries, which invariably leads to the patient's arrest.
The Violations Documenting Centre, a partner of the activist network, said 250 doctors and pharmacists have been arrested since the anti-regime protests erupted in mid-March, 25 of them in the past few weeks.