Airstrikes by the Russian-backed Bashar Assad regime on Syria’s northwestern Idlib province, the last opposition bastion, have increased recently as the latest attack by Russian jets claimed the lives of at least one civilian and injured two others.

United Nations Secretary-General Antonio Guterres strongly condemned the recent wave of attacks in northwest Syria, which have killed and injured dozens of civilians, U.N. Deputy Spokesperson Farhan Haq said Monday.

The U.N. chief reiterated his call for a nationwide cease-fire citing the aerial attacks near the border as well as artillery strikes on a hospital in western Aleppo Governorate on March 21, reports of shelling of a residential neighborhood in Aleppo city causing civilian casualties and airstrikes close to densely populated areas with camps for displaced people, Haq said.

Mark Cutts, a U.N. deputy regional humanitarian coordinator for the Syria crisis, called the attacks "extremely worrying" because they endangered the lives of the area's most vulnerable population.

U.N. Resident Coordinator and Humanitarian Coordinator for Syria Imran Riza similarly decried the attacks saying: "A number of attacks in Syria in past days have claimed civilian lives and hit civilian infrastructure. I strongly condemn these attacks. Civilians must be protected, and I emphasize again the obligation of parties to ensure the safety of civilians and civilian facilities."

The U.S. also sharply condemned Monday the Russian and Syrian regime airstrikes over the weekend that targeted a hospital and killed several civilians.

State Department Spokesperson Ned Price said the coordinates of Atareb Surgical Hospital had previously been shared with a U.N. entity intended to prevent attacks on civilian infrastructure.

The hospital was struck by artillery shelling Sunday morning, injuring five staffers and killing six patients, including a child, according to the Syrian American Medical Society. The hospital, which had been providing badly-needed services, sustained extensive damage and has been shuttered.

Another airstrike by Russia on the al-Bab border crossing with Turkey killed one civilian and injured two others.

"Bab al-Hawa remains the only U.N.-authorized humanitarian border crossing in Syria and remains the most efficient and effective way to provide life-saving humanitarian assistance to approximately 2.4 million Syrians every month," Price said.

"Civilians, including civilian medical personnel and facilities, must never be the target of military action. This violence must stop, we reiterate our call for a nationwide cease-fire," he added.

The area along the border with Turkey in opposition-held northwestern Syria had been considered one of the safest spots in the conflict-stricken region and had attracted aid groups who located their offices and warehouses there.

"Many of the camps are in that area, about a million people in camps around that area. They are highly vulnerable when airstrikes and shelling happen," Cutts told The Associated Press (AP). "It is also the area where many of the humanitarian organizations have offices and warehouses. They put their warehouses and offices there thinking that was the safest part of Idlib. So when that starts coming under attack that is extremely worrying."

Turkey and Russia support rival parties in Syria’s 10-year conflict. The countries reached a cease-fire deal last March that stopped a Russian-backed regime offensive on Idlib.

The Syrian Network for Human Rights told Daily Sabah that the Assad regime and its allies have carried out at least 75 attacks since Turkey launched Operation Spring Shield and brokered the cease-fire last March.

Idlib-based journalist Salwa Abdul-Rahman said one of the strikes hit an area near the town of Sarmada, setting afire trucks used by aid workers to distribute assistance.

"The targeted locations were civilian with no military presence," she said.

The White Helmets Syrian civil defence group issued a statement right after the attack on the hospital and underlined that "this crime is a continuation of the regime and Russia’s systematic policy of targeting medical facilities and hospitals, intending to deprive civilians of these vital services."

It added that the bombing of the hospital came at a time when the world is suffering from a great shortage of medical personnel in the face of the COVID-19 pandemic.

Turkey’s Defense Ministry blamed Syrian regime forces for the attack, saying it left several people wounded.

For years, the Assad regime has ignored the needs and safety of the Syrian people, only eyeing further gains of territory and crushing the opposition. With this aim, the regime has for years bombed civilian facilities such as schools, hospitals and residential areas, causing the displacement of almost half of the country's population.