As tons of desperately needed medical supplies await clearance to be flown into Yemen, aid workers warned Tuesday of an unfolding humanitarian crisis, saying at least 560 people, including dozens of children, have been killed, mostly in a Saudi-led air campaign and battles between Shiite rebels and forces loyal to the embattled president.

More than 1,700 people have been wounded and another 100,000 have fled their homes as fighting intensified over the past three weeks, the World Health Organization said.

The Red Cross shipment would be the first to reach Yemen since the start of the Saudi-imposed air blockade. Sitara Jabeen, a Geneva-based spokeswoman for the International Committee of the Red Cross, said a cargo plane with 17 tons of medical supplies was in the Jordanian capital, Amman, awaiting the go-ahead from coalition forces to land in Sanaa, hopefully today. Another 35 tons of supplies were also ready for shipment, she said.

“If these medical supplies do not reach Yemen, then unfortunately we are afraid many more people will die,” Jabeen said.

She said a surgical team was also awaiting clearance to dock in the embattled Yemeni port of Aden, where heavy fighting Monday left streets littered with bodies.

The fighting pits allies of Yemen’s president, Abed Rabbo Mansour Hadi, against Iranian-backed Shiite rebels, known as Houthis, and allied military units loyal to ousted President Ali Abdullah Saleh.

The Saudi-led air campaign, which supports Hadi, now in its 13th day, so far has failed to stop the Houthis’ advance on Aden, Yemen’s second-largest city. Hadi declred it the provisional capital before he fled the country for Saudi Arabia as the rebels closed in two weeks ago.

WHO said Tuesday that at least 560 people had been killed and 1,768 wounded — many of them civilians — since the rebels and their allies launched an intensified land grab on March 19. At least 293 have died since the March 26 start of the Saudi-led air campaign.

The dead include at least 74 children, the U.N. children’s agency said. At least 44 children have been wounded.

Comprehensive casualty figures are difficult to collect and verify because of the ongoing violence, and aid agencies warned the overall death toll is likely far higher.

The Saudi campaign has turned Yemen into a new proxy war between the kingdom and Iran, which has backed the Houthis, though Tehran denies aiding the rebels militarily.

Civilians have paid a heavy toll for the violence that mushroomed from an internal power struggle into a regional war. Children have been especially vulnerable, said UNICEF’s Yemen representative, Julien Harneis.

“They are being killed, maimed and forced to flee their homes, their health threatened and their education interrupted,” Harneis said in a statement.

Humanitarian groups say they are running out of supplies and have called for a temporary halt to the fighting to allow medical teams and fresh medical supplies to arrive in the country and for residents to identify and bury their dead.