Condemnation has mounted over deadly air strikes on a camp for displaced people in northern Syria's Idlib, as a ceasefire that was due to end on Saturday was extended by 72 hours.

Women and children were reported to be among 30 killed in Thursday's raids near the Turkish border, which also wounded more than 50 others.

"I came out and I saw my son bleeding in his abdomen and his shoulder, and I couldn't find my daughter and her children and then I found her dead. Praise be to God," Um Mohamed, a survivor, told Al Jazeera.

"I have only this girl left, she is 11 years old."

Another survivor told Al Jazeera that there was no safe place for refugees.

"Where are we supposed to go? Tell me a safe place I can go to. Death is the same, if it is here or back home we all die the same," Mostafa said.

A video posted online showed emergency workers covering charred victims with blankets and carrying them away.

Dozens killed in air strike on refugee camp near Idlib

In pictures: Death rains down on Syria as ceasefire wobbles

Ban Ki-moon, the United Nation secretary-general, said that he was "outraged" by the attack and demanded those responsible must face justice.

The Syrian regime and its Russian ally, which have carried out intense air strikes in Aleppo and surrounding areas in the past few weeks, denied involvement in the deadly attack.

A tenuous ceasefire has been in place since February brokered by Russia and the United States, but Damascus has continued to bomb rebel-controlled areas in Aleppo that was not part of the deal. Nearly 300 people have been killed in the recent upsurge of violence.

Opposition activists say the camp was targeted by two air strikes. But the Syrian military said on Friday that it did not target the camp, state news agency SANA reported. 

Cooking utensils are seen in burnt tents at a camp for internally displaced people near Sarmada in Syria's Idlib province [Reuters]

Under-Secretary-General for Humanitarian Affairs, Stephen O'Brien, also called for an immediate, impartial and independent investigation into the air strikes.

Deadly attack hits hospital in Syria's Aleppo

"All parties to this appalling conflict should understand that they will one day be held accountable for violations of international humanitarian and human rights law."

The strikes in Idlib province, which is controlled by al-Nusra Front and rebel allies, came as a 48-hour ceasefire took hold in Aleppo to the east.

That truce was due to end early on Saturday, but Moscow and Washington announced that it would be extended by 72 hours.

Elsewhere in Syria, in Hama province, regime forces launched an assault against a prison in the central city of Hama aimed at ending a mutiny, the UK-based Syrian Observatory for Human Rights said on Saturday.

The mutiny began on Monday after an attempt to transfer inmates to the military-run Saydnaya prison near Damascus.

Human Rights Watch said it had received WhatsApp messages from inmates saying that security forces "were attempting to storm their prison block, using tear gas and rubber bullets".

It said the assault "raises major concerns about possible excessive use of force".

The Aleppo halt in fighting is part of international efforts to revive the February ceasefire and galvanise peace talks to end a five-year war that has killed more than 270,000 people and displaced millions.

Source: Al Jazeera and agencies