It follows reports of recent massacres carried out by Syrian troops and their allies in and around the city of Banias.
The mass killings "should spur the international community to act to find a solution to the conflict, and to ensure those responsible for serious human rights violations are made to account for their crimes", the office of the UN High Commissioner for Human Rights said.
Rights monitors say at least 62 civilians, including 14 children, were killed in an assault on a Sunni neighbourhood of Banias earlier this month.
And at least 50 people were killed in the nearby village of Bayda.
"I am appalled at the apparent killing of women, children and men in the
village of al-Bayda, and possibly elsewhere in the Banias area,” Pillay said.
She said the killings seemed “to indicate a campaign targeting specific communities perceived to be supportive of the opposition”.
Speaking in Geneva, her spokesman Rupert Colville described "harrowing images of piles of bloodied and burned bodies, including small children and babies".
He said, if verified, these "indicate a complete lack of regard for the lives of civilians".
"There needs to be a careful investigation of each and every incident like this. We should not reach the point in this conflict where people become numb to the atrocious killing of civilians," Pillay said in her statement.
The UN rights chief lamented the serious human rights violations that have taken place in Syria during more than two years of spiralling violence, which has cost more than 70,000 lives.
She reiterated her belief that "war crimes and/or crimes against humanity have been committed" and once again called for the deadlocked UN Security Council to refer the situation to the International Criminal Court.