ADEN (Reuters) - At least 13 people were killed on Tuesday in the first air strikes by a Saudi-led coalition on the Yemeni capital in five months, residents said, as the head of the U.N. expressed concern about the escalation in the fighting.

An employee walks inside a a snack food factory after a Saudi-led air strike hit it in Sanaa, Yemen, August 9, 2016. REUTERS/Khaled Abdullah?

Fighting has intensified since U.N.-sponsored peace talks between the Houthis, backed by forces loyal to former President Ali Abdullah Saleh, and the internationally recognized government ended on Saturday without an agreement.

Medics put the death toll at 13. Most of the casualties were women working at the al-Aqel potato chip factory in the Nahda district of the capital.

Residents said the factory was inside an army maintenance camp that had been hit by repeated air strikes since fighting began in March last year.

The Houthi-run news agency has put the death toll at seven, including five women, and said 13 people were injured.

Footage from the scene showed firefighters battling flames inside the factory, while rescue workers carried casualties wrapped in clothes away.

Residents and local Yemeni media also reported air strikes in the Red Sea port city of Hodeida and other parts of Yemen.

Slideshow ( 4 images )

The Saudi-led coalition is backing Yemeni forces loyal to the government of President Abd-Rabbu Mansour Hadi, who are trying to oust Iran-allied Houthi forces from the capitol, Sanaa. Hadi was forced to flee Yemen to Saudi Arabia as Houthi forces advanced on his headquarters in Aden in March 2015.

United Nations Secretary-General Ban Ki-moon said he was concerned about the reports of increased fighting, a U.N. spokesman said on Tuesday, but added the world body was unable to independently verify reports of civilians deaths.

“What is clear, however, is that the reported escalation in fighting exacerbates the already dire humanitarian and human rights situation and the suffering of the Yemeni people,” the spokesman, Farhan Haq, said in a statement.

FLIGHTS SUSPENDED

At least nine civilians were killed by coalition air strikes in Nehm district, east of Sanaa on Sunday night, residents said on Monday, as forces loyal to Hadi forces stepped up an offensive in the area.

The United Nations children’s Fund said in a statement on Tuesday that four children were “reportedly killed” on Sunday in Nehm but did not say who was behind the attacks. UNICEF said that it had verified that 1,121 children have been killed and another 1,650 injured since the conflict began in 2015.

Coalition also forced the suspension of flights into Sanaa International Airport for 72 hours from late on Monday, an airport official and aid agency sources said.

The head of the Houthi delegation to the Kuwait peace talks, who was returning home after the negotiations ended, said in a Facebook posting that he and his team were stranded in Oman by the flight ban.

In a separate development, residents in Azzan in the province of Shabwa in southern Yemen said Al Qaeda militants had dismantled their checkpoints and had withdrawn from the city on Tuesday following air strikes - apparently by the Saudi-led coalition - targeting their positions there.

The militants took advantage of the country’s wartime chaos to seize control of much of southern Yemen, but have suffered military setbacks inflicted by coalition-backed local forces.