The resolution was passed by the 47-member state council with 41 votes in favour, two abstentions and three — Russia, China and Cuba — against.
“The Syrian authorities have manifestly failed in their responsibility to protect the Syrian population, and have committed gross human rights violations which may amount to crimes against humanity,” said a Danish envoy on behalf of the European Union while presenting the resolution.
“Therefore, this resolution focuses on accountability for human rights violations committed by the Syrian authorities. Perpetrators must be held to account,” he added.
“Given the gravity of the situation, we have no choice but to extend the mandate of the commission of inquiry.”
A commission of inquiry dispatched by the council said in February it had handed to the UN rights chief a list of regime officials suspected of crimes against humanity.
It also documented a “widespread and systematic pattern of gross violations” committed by Syrian forces.
Friday’s resolution asked the commission to continue reporting back about the situation during the council’s June session.
As part of its mandate to catalogue abuses, the investigators were also asked for “assessment of casualty figures” that should be published periodically.
Syria’s envoy angrily rejected the resolution, saying it “reflects a politicisation and a biased viewpoint” of the council.
Monitors say more than 9,100 people have been killed in the unrest that started with peaceful protests in Mar 2011 before turning into an armed revolt, faced with a brutal crackdown which has cost dozens of lives each day.