Damascus: World powers piled pressure on Syria to allow observers to monitor spiraling deadly violence as activists condemned rights violations on the anniversary of International Human Rights Day on Saturday.

Activists said 41 civilians were killed on Friday in flashpoint cities across Syria as the opposition warned the regime was planning a "massacre" in the protest hub of Homs, where another civilian was killed on Saturday.

"The world celebrates human rights as human rights are being violated in Syria," the opposition Syrian Revolution 2011 said in a message posted on its Facebook page.

UN Human Rights Commissioner Navi Pillay has said that at least 4,000 people have been killed in a government crackdown on dissent in Syria since the anti-regime protest movement started in March.

Pillay is to brief the UN Security Council about Syria and the wider Middle East at a meeting on Monday -- her second address to the world body since August when the number of dead was estimated at more than 2,000.

"Now it is more than 4,000. Lives could have been changed if action had been taken sooner. It is not for me to determine what kind of action, it is for the Security Council," she told a UN news conference on Friday.

Syrian President Bashar al-Assad has refused to let investigators from two UN human rights inquiries enter Syria, and his regime is resisting Arab League calls to accept monitors despite being hit by crippling sanctions.

As the death toll mounted Britain and the United States expressed fresh concerns, and Washington urged Syria to allow independent monitors into the country.

Damascus, which blames "armed terrorist gangs" for the violence, meanwhile appealed to the international community to help it find an "honourable exit" to the crisis and stem the flow of weapons into Syria.

"We are appealing to the outside world and our brothers in the Arab world to help Syria (prevent the) channelling (of) weapons" into the country, foreign ministry spokesman Jihad Makdisi said on Friday, speaking in English.

"If we all work together we can find an honourable exit to the crisis."

The Syrian Observatory for Human Rights said at least 41 civilians, including seven children, were shot dead by Syrian security forces in the capital Damascus and the restive central city of Homs on Friday.

Thirteen people were killed in the Homs region, five in the restive city of Hama, 18 around Damascus, two in Daraa, cradle of the protest movement, and three in the northwestern province of Idlib, the watchdog said.

(Agencies)