UNITED NATIONS, Dec. 21 (Xinhua) -- A plane charted by the United Nations Children's Fund (UNICEF) landed in Yemen's capital city of Sana'a on Thursday, delivering nearly six million doses of essential vaccines for millions of children at risk of preventable diseases.

"Vaccinating children in Yemen now is critical to protect them from preventable diseases and death. It is vital that vaccines and other lifesaving supplies for children continue to flow into Yemen and across the country unimpeded. They are a lifeline for millions of children," said Meritxell Relano, UNICEF Representative in Yemen.

The current diphtheria outbreak has reportedly infected over 300 people and killed 35, with most cases and deaths being reported among children.

Since 2015, Yemen has been in a conflict between forces loyal to President Abdrabbuh Mansour Hadi and those allied to the Houthi rebel movement.

The country is in the grips of the world's worst humanitarian crisis, with restrictions on fuel and food imports further complicating emergency response.

UNICEF reiterates its call on all parties to allow unhindered humanitarian access to all of Yemen's land, sea and air ports and to facilitate the distribution of lifesaving assistance for children inside the country.