The United Nations human rights office has called for a thorough probe into the allegations of widespread abuses committed by Syrian authorities during their violent crackdown against protesters, including the excessive use of force against civilians, arbitrary detentions and torture.

"The most egregious reports concern the use of live ammunition against unarmed civilians, including from snipers positioned on rooftops of public buildings, and the deployment of tanks in areas densely populated by civilians," states a preliminary report prepared by the Office of the High Commissioner for Human Rights (OHCHR) that was released today.

"As of mid-June, the number of those killed during such incidents is believed to have exceeded 1,100 persons, many of them unarmed civilians; among them were women and children," it added.

Syrian authorities have been widely criticised for their bloody repression of the protests, which are part of a broader uprising this year across North Africa and the Middle East that has already toppled the long-standing regimes in Tunisia and Egypt and led to ongoing conflict in Libya.

Given that OHCHR has been unable to deploy staff on the ground in Syria, the report, which covers the period from 15 March to 15 June, is based on information received from UN partners, human rights defenders, civil society groups, media groups and a small number of victims and eyewitnesses from Syria.

In addition to the use of live ammunition, arbitrary detentions have been carried out by the Syrian authorities on a "massive" scale, with reports indicating that up to 10,000 people have been detained since mid-March.

The report adds that while women and children were among those detained, human rights defenders, political activists and journalists were particularly targeted.

OHCHR has also received information indicating that Syrian security forces have perpetrated acts of torture and other cruel and inhuman treatment against detainees, resulting in death in custody in some cases.

Reports of alleged violations of the rights to freedom of assembly, expression, and movement, and of the rights to food and health have also been received.

"The material currently before the High Commissioner is a matter of grave concern and reflects a dire human rights situation in the Syrian Arab Republic. The alleged breaches of the most fundamental rights on such a broad scale require thorough investigation and, with respect to the perpetrators, full accountability," states the report.

High Commissioner Navi Pillay also renewed her call to the Syrian Government to grant access to the country for the fact-finding mission established by the UN Human Rights Council.