The intensification of fighting in northern Syria has been described by the U.N. as horrific and requiring immediate intervention.

Rebel opposition forces in Syria defended on Friday a heavy attack by the forces of the Syrian President, Bashar al-Assad, in the northern Syrian province of Idlib, which is considered to be the last rebel stronghold in the country.

According to Syrian News Agency, the Syrian army engaged in heavy battles with the opposition fighters overnight Friday, after the opposition elements fired several shells on the Hamada countryside, to the north.

In the meantime, a statement by the opposition read that the opposition fighters were able to take over three main villages in the Hamada countryside, late on Thursday night. The statement added that the Syrian army had been inflicted with many losses as the fighting ensued intensively, on Friday.

The latest round of fighting in the north of the country is said to be the toughest between the Syrian army and the rebels in both Idlib and Hama provinces.

Medical care organizations including Union of Medical Care and Relief Organizations which operate in areas controlled by the rebels revealed that the fighting had forced 55 medical facilities to shut down since April.

The Idlib-based opposition forces are said to be linked to the Liberation Front of Levant or the former Al-Nusra Front, which are both believed to belong to the Islamic State in Iraq and Levant, widely known as ISIL.

Based on recent agreements between Russia and neighboring Turkey, the Turkish military has deployed troops in twelve positions in Idlib and in other northern areas that are controlled by the opposition fighters.

Commenting on the current spate of fighting, the U.N. office for the coordination of humanitarian affairs confirmed that tens of medical care centers and schools were damaged. The office described the situation as horrific and requiring immediate intervention.

Since 2011, the Arab Republic of Syria, home to nearly 19 million residents, has endured through a civil war that was sparked by mass protests, demanding social and economic reforms.

Since then, hundreds of thousands have been killed and injured, while hundreds of thousands more have been displaced. In recent years, Russia became a key ally for the Syrian regime, intervening in the war and helping Syria defeat the armed opposition groups.