The United Nations voiced fresh alarm on Friday at consistent reports of executions and torture of civilians including children in Syria as well as killings of demonstrators in pro-democracy rallies.

The U.N. Committee against Torture cited rife or systematic attacks against (the) civilian population, including the killing of peaceful demonstrators.

Syria faces increasing international pressure over its bloody crackdown on popular unrest. Damascus had until the end of the day Friday to sign an Arab deal allowing monitors into the country or incur sanctions.

More than 3,500 people have been killed since March, according to the United Nations, and activists say that more than 30,000 have been arrested, including families of dissidents.

The U.N. committee said reports of children suffering torture and mutilation during detention were of particular concern, and that Syrian authorities had been acting with total impunity in what it called gross and pervasive human rights violations.

The committee, composed of 10 independent experts, called on the government of President Bashar al-Assad to report back by March 9 on measures taken to halt abuses which it said were allegedly conducted under direct orders from public authorities.

The committee's chairman, Claudio Grossman, also voiced concern for the extrajudicial, summary or arbitrary executions, arbitrary detention by the police forces and the military; and enforced and involuntary disappearances.

Grossman, an expert from Chile, told a news briefing: Needless to say the serious massive violations of human rights take place in a context of total and absolute impunity. There haven't been investigations on this matter.

(Reporting by Stephanie Nebehay; Editing by Alessandra Rizzo)