Four children have been killed in a Saudi-led coalition airstrike on a remote hospital in Yemen, according to Save the Children.

Three others were killed during the attack on Tuesday, and at least eight others were wounded after the missile struck a petrol station near the entrance of the rural hospital, around 100km from Saada in the country's northwest, the charity said. Two adults remain unaccounted for.

A health worker and their two children were among those killed.

The hospital – supported by the charity – had just opened for the day and many patients and staff were said to be arriving on the busy morning.

“We are shocked and appalled by this outrageous attack. Innocent children and health workers have lost their lives in what appears to have been an indiscriminate attack on a hospital in a densely populated civilian area,” said Kevin Watkins, CEO of Save the Children, who has visited some of the charity's health facilities in Yemen.

“Attacks like these are a breach of international law.”

Children suffering from acute malnutrition in Yemen Show all 17 1 /17 Children suffering from acute malnutrition in Yemen Children suffering from acute malnutrition in Yemen Doctors take some blood of Yemeni Yousef Abdullah Bakhit Ali, 13, suffering from severe acute malnutrition. With ongoing and unending conflict in Yemen, humanitarian situation continues to deteriorate across the country Unicef/Huwais Children suffering from acute malnutrition in Yemen A doctor weighs Yemeni baby Yahya Hamoud Ali Al Huzef, 9 months suffering from malnutrition Unicef/Huwais Children suffering from acute malnutrition in Yemen Ali Mohammed Ahmed Jamal,12 years old and suffering from severe acute malnutrition. He arrives with his family at a Unicef supported treatment centre in a hospital in Sanaa Unicef/Huwais Children suffering from acute malnutrition in Yemen A doctor measures the arm of Yemeni Ali Mohammed Ahmed Jamal, 12, who is suffering from malnutrition at a treatment centre in a hospital in Sanaa Unicef/Huwais Children suffering from acute malnutrition in Yemen There are over 400,000 severely malnourished children in need urgent lifesaving assistance in Yemen Unicef/Abdulhaleem Children suffering from acute malnutrition in Yemen Ali Mohammed Ahmed Jamal is weighed Unicef/Huwais Children suffering from acute malnutrition in Yemen A doctor measures the arm of baby Yahya Hamoud Ali Al Huzef Unicef/Huwais Children suffering from acute malnutrition in Yemen Unicef are currently working to reach 275,000 malnourished children with critical life-saving supplies and care for over 5 million people with safe and clean water to stop the spread of life-threatening diseases Unicef/Huwais Children suffering from acute malnutrition in Yemen Yahya Hamoud Ali Al Huzef with his family in his house in the outskirts of the capital Sanaa Unicef/Huwais Children suffering from acute malnutrition in Yemen The country is on the brink of famine and children's chances of survival are becoming slimmer by the day Unicef/Abdulhaleem Children suffering from acute malnutrition in Yemen Ali Mohammed Ahmed Jamal has his arm measured Unicef/Huwais Children suffering from acute malnutrition in Yemen Unicef are currently working to provide nearly 1 million children with vaccines and healthcare Unicef/Huwais Children suffering from acute malnutrition in Yemen Doctors take some blood of Yemeni Yousef Abdullah Bakhit Ali, 13 years old suffering from severe acute malnutrition at a treatment centre in a hospital in the capital Sanaa on November 2, 2018. (Release obtained) With ongoing and unending conflict in Yemen, humanitarian situation continues to deteriorate across the country. There are over 400,000 severely malnourished children in need urgent lifesaving assistance in Yemen. The country is on the brink of famine and childrenâ€™s chances of survival are becoming slimmer by the day. UNICEF are working with partners around-the clock to save children suffering from malnutrition and disease. We are currently working to reach: â€¢ 275,000 malnourished children with critical life-saving supplies and care â€¢ Over 5 million people with safe and clean water to stop the spread of life-threatening diseases â€¢ Nearly 1 million children with vaccines and healthcare â€¢ 9 million people with emergency cash assistance to help families buy basic commodities so they can survive Â© UNICEF/UN0253367/ Huwais Unicef/Huwais Children suffering from acute malnutrition in Yemen Unicef are working with partners around-the clock to save children suffering from malnutrition and disease Unicef/Abdulhaleem Children suffering from acute malnutrition in Yemen Unicef are currently working to provide 9 million people with emergency cash assistance to help families buy basic commodities so they can survive Unicef/Huwais Children suffering from acute malnutrition in Yemen Ali Mohammed Ahmed Jamal is suffering from malnutrition Unicef Children suffering from acute malnutrition in Yemen On 31 October 2018 in Yemen, the Al Thawra Hospital in Hodeidah where children are being treated for severe acute malnutrition. UNICEF Regional Director for Middle East and North Africa Geert Cappelaere visited Yemen from 29 October through 1 November 2018. As of 30 October 2018, over 11 million children â€“ 80 per cent of all children in the country â€“ require humanitarian assistance, due to the impact of the ongoing conflict. Worsening years of underdevelopment, attacks against civilians and civilian infrastructure and lack of salary payments for most civil servants have pushed basic services for children to the brink. Children face food shortages, disease, displacement and an acute lack of access to basic social services. One out of three children in Yemen is at risk of acute malnutrition. Â© UNICEF/UN0253574/Abdulhaleem Unicef/Abdulhaleem

The attack comes as the devastating conflict enters its fifth year, which the UN says had left at least 10,000 dead, displaced more than 3 million people, and left most of the population food insecure.

The civil war pits Houthi rebels – who control northern Yemen – against the Saudi-led coalition backing the internationally recognised government. UN experts have accused both sides of committing possible war crimes.

The damage after a missile struck a gas station near the entrance to Kitaf rural hospital 100 km from the city of Saada, Yemen (SAVE THE CHILDREN)

Some 37 children have been killed per month in bombs in the last year, according to Save the Children.

The Saudi-led coalition has been accused by rights groups of targeting hundreds of hospitals as part of its aerial campaign against rebels in the north. The coalition denies these claims.