NEW YORK (REUTERS) - More than 700 civilians - including 52 children - have been killed in Ukraine since Russia invaded three weeks ago, but the "actual number is likely much higher," UN political affairs chief Rosemary DiCarlo told the Security Council on Thursday (March 17).

"Most of these casualties were caused by the use in populated areas of explosive weapons with a wide impact area. Hundreds of residential buildings have been damaged or destroyed, as have hospitals and schools," Ms DiCarlo said.

She told the 15-member council that the UN human rights agency has recorded 726 deaths, including 52 children, and 1,174 people injured, including 63 children, between Feb 24 and March 15.

Ms DiCarlo did not specify who was to blame.

"The magnitude of civilian casualties and the destruction of civilian infrastructure in Ukraine cannot be denied. This demands a thorough investigation and accountability," she said.

The World Health Organisation has verified 43 attacks on healthcare in Ukraine that have killed 12 people and injured dozens more, including health workers, WHO Director-General Tedros Adhanom Ghebreyesus told the Security Council.

"In any conflict, attacks on healthcare are a violation of international humanitarian law," Dr Tedros told the council, without specifying who was to blame.

Ukraine and its Western allies accuse Moscow of attacking civilians. Russia has called its military actions in Ukraine a "special operation" and denies attacking civilians, saying it is targeting Ukraine's military infrastructure.