UNITED NATIONS (Reuters) - It is “highly probable” the government of Syria or its allies carried out attacks on three healthcare facilities, a school and a refuge for children in northwest Syria last year, according to a summary of an internal United Nations inquiry seen by Reuters on Monday.

FILE PHOTO: U.N. Secretary General Antonio Guterres makes a statement at U.N. headquarters in New York City, New York, U.S., September 23, 2019. REUTERS/Yana Paskova/File Photo

The inquiry also found it “probable” that a deadly attack on a Palestinian refugee camp in Syria’s Aleppo was carried out either by armed opposition groups or by Hayat Tahrir al-Sham, a jihadist alliance formerly known as Nusra Front.

Syrian President Bashar al-Assad’s forces, backed by Russia, began an offensive early last year on the last major insurgent stronghold in northwest Syria. Russia and Syria have said their forces do not target civilians or civilian infrastructure.

The Russian and Syrian missions to the United Nations did not immediately respond to a request for comment on the summary of the U.N. report, which Secretary-General Antonio Guterres submitted to the 15-member Security Council on Monday.

“The impact of the hostilities on civilian and humanitarian sites in north-west Syria is a clear reminder of the importance for all parties to the conflict to observe and ensure respect for international humanitarian law,” Guterres wrote in a letter to the council.

“According to numerous reports, the parties have failed to do this,” he said.

Under pressure from two-thirds of the Security Council, Guterres announced in August that the world body would investigate attacks on U.N.-supported facilities and other humanitarian sites in northwest Syria.

The locations of the U.N.-supported facilities and other humanitarian sites had been shared with the warring parties in a bid to protect them. However, the United Nations has questioned whether it made them a target.

Guterres noted that the members of the board of inquiry were unable to visit Syria to investigate as the government of Syria did not respond to repeated requested for visas. The attacks investigated by the board took place in April, May and July.

Fighting has calmed in the northwestern region after Turkey, which backs rebels opposed to Assad and ramped up its deployment earlier this year, agreed on a ceasefire with Russia a month ago. The fighting has displaced nearly 1 million people in Idlib.

A crackdown by Assad on pro-democracy protesters in 2011 led to Syria’s civil war.