An estimated 540 people have been killed in Yemen and 1,700 wounded by violence since 19 March 2015, a UN representative said.

"Estimations from 6 April, as of yesterday, are: 540 people have been killed and some 1,700 wounded by the violence in Yemen since 19 March," World Health Organization (WHO) spokesman Christophe Lindmeier told reporters at a news briefing.

More precisely, the United Nations says 549 people were killed and more than 1,700 wounded in the two weeks leading up to April 3. That figure includes at least 217 civilian deaths and 516 civilians wounded, many of them in suicide bombings at two Sanaa mosques on March 20 which killed 137 people.

The Iranian-allied Houthis and the pro-Saleh army units took over Sanaa in September 2014 and last month launched an advance on the Southern city of Aden, a stronghold of President Abd-Rabbu Mansour Hadi, who has now fled the country and is based in Saudi Arabia.

According to UNICEF, since the fighting begun, at least 74 children have been killed, nearly 50 wounded, but these figures are considered to be highly underestimated.

"74 children are known to have been killed and 44 children maimed so far, since the fighting began on March 26. But we say, we are aware that these are conservative figures and we believe that the total number of children killed is much higher," UNICEF spokesman Christophe Boulierac said.

Boulierac insisted that children in Yemen were already facing extremely precarious living conditions, with a lack of drinkable water and health facilities that were already under immense pressure.

"Childhood in Yemen is characterized by a situation of chronic vulnerability, whether it be regarding malnutrition, access to health care, so the increase in violence does affect health and education infrastructures. Therefore, there will be, there already are indirect deaths due to a lack of supply of medical equipment and I can't forget to also name the psycho-emotional damages which are very obvious," he said.

According to WHO, between 1-4 April, three medical workers from the Yemen Red Crescent Societies were shot and killed while they were responding to emergency calls. Three ambulances from the ministry of public health were taken by armed forces and have since been used for other purposes.

While the International Committee of the Red Cross aims to fly two planes carrying a total of 48 tonnes of medical help and other aid to Yemen over the next two days, both UNICEF and WHO have insisted on the difficulty to get aid and assistance into the country.

Since the conflict has escalated, eight inter-agency health kits have been provided for about 240,000 people throughout the country, but they came from warehouses in Sanaa, Aden and Hodeidah. Bringing new material in is "the biggest challenge", the agencies said.