Sanaa (AFP) - The International Committee of the Red Cross said Tuesday it was "extremely concerned" by a growing number of corpses being abandoned in the war zones of Yemen.

"With the escalation of the fighting, more casualties are being left behind owing to the increased danger associated with retrieving the wounded and the dead," said Nourane Houas, head of the ICRC's Protection Department in war-ravaged Yemen.

"International humanitarian law requires that dead bodies be treated properly and with respect," the ICRC said in a statement.

Houas urged all sides in the conflict "to respect the dignity of the dead and to allow their swift recovery, while taking all feasible measures to ensure their proper identification and their handover to the families".

Under Islam, the predominant religion in Yemen, the dead should be buried the same day whenever possible.

"Failure to identify the dead puts them in the ranks of the missing, and prevents the families from mourning," said Houas.

The ICRC said it has helped retrieve more than 407 dead bodies since March.

Fighting has intensified since that month after Iran-backed Shiite Huthi rebels and their allies entered President Abedrabbo Mansour Hadi's last refuge, the southern port city of Aden.

Hadi fled the country and on March 26, Saudi Arabia led a coalition of Arab states in carrying out air strikes against rebel positions across Yemen.

The World Health Organization says the conflict had claimed 4,345 lives from March up until August 5.

Half of those killed are civilians, and 80 percent of Yemen's 21 million people need aid and protection, according to UN figures.