The United Nations human rights chief says UN experts will investigate the deadly air strikes that killed at least 28 people at a refugee camp in Syria on May 5.
Zeid Raad al-Hussein said on May 6 that "it is extremely unlikely that these murderous attacks were an accident" and said they could "amount to a war crime."
He added that reports the attack was carried out by Syrian planes still had to be verified.
The Syrian military denied its planes were involved in the attack. It suggested opposition forces were responsible.
France and several other countries had earlier condemned the attack in northern Syria and called for an investigation.
The French Foreign Ministry said in a statement that the attack in Idlib Province near the Turkish border was a "revolting and unacceptable act that could amount to a war crime or crime against humanity."
The tent camp houses Syrians who have fled the country's more than five-year-long civil war.
Russia's Defense Ministry said neither its planes nor any other fighter jets had flown over the Sarmad area near the camp at the time of the attack.
Fighting also continued in other parts of northern Syria despite a temporary deal for a truce in the city of Aleppo.