Syria's military denied Friday any involvement in air strikes that killed at least 28 civilians in a camp for displaced people near the Turkish border, state media said.

"There is no truth in the information in some media that the Syrian air force targeted the displaced camp in Idlib province" on Thursday, the SANA news agency quoted the military as saying.

It accused rebels of targeting civilians.

The Syrian Observatory for Human Rights, a British-based monitor, said women and children were among the 28 civilians killed at the camp in the village of Al-Kammouna.

Mamun al-Khatib, director of the Aleppo-based pro-rebel Shahba Press news agency, accused "regime aircraft" of firing missiles at the camp.

The United States and the European Union denounced the raid, while the United Nations' top aid official demanded an immediate investigation.

Stephen O'Brien, the UN under-secretary general for humanitarian affairs, said that if the air strikes were found to be "a deliberate targeting of a civilian structure", it could amount to a war crime.

Thousands of Syrians have fled recent fighting in the northern province of Aleppo and camps for the displaced have been set up along the Turkish border.

Idlib province is controlled by Syria's Al-Qaeda affiliate Al-Nusra Front and rebel allies.

Al-Nusra is not included in a February 27 ceasefire between the regime and non-jihadist rebels.

More than 270,000 people have been killed and millions displaced since Syria's conflict started in 2011.