SANAA, Yemen (AP) -- The U.N. human rights office and the international Red Cross say they are alarmed by the high civilian causalities in the violence in Yemen, where airstrikes by a Saudi-led coalition have been targeting Shiite rebels since last week.


Tuesday's statement from Geneva said U.N. human rights staffers in Yemen have verified that at least 19 civilians died when airstrikes hit a refugee camp in northern Yemen, with at least 35 wounded, including 11 children.


There were different reports of casualty figures from Monday's strike. The Houthi rebels said 40 people died while Doctors Without Borders tweeted that 29 people were killed.


The International Committee of the Red Cross is appealing to the parties in the conflict to allow delivery of medical supplies to the wounded.


THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.


Saudi-led coalition warplanes pounded Yemen's Shiite rebels for a sixth day on Tuesday, destroying missiles and weapons depots and for the first time using warships to bomb the rebel-held airport and eastern outskirts of the port city of Aden.


The airstrikes' campaign by Sunni Arab states, which began last week, is meant to halt the advance by the Shiite rebels known as the Houthis who have overrun the country and forced Yemen's president to flee abroad.


Overnight and into early hours Tuesday, the coalition bombed the Iran-backed rebels around the capital, Sanaa, according to Yemeni military officials. The strikes targeted Houthi positions and camps, as well as weapons depots controlled by the rebels, the officials said.


Meanwhile, Iran said it sent an aid shipment to Yemen, according to the official IRNA news agency - Tehran's first such delivery since the Saudi-led airstrikes started last Thursday. The aid contained 19 tons of medicines and medical equipment and two tons of food provided by the Iranian Red Crescent, IRNA said.


The agency reported that the aid was delivered by air early Tuesday but did not say where the cargo landed. The coalition has bombed a number of rebel-held airports and has announced it is in full control of Yemen's airspace.


The conflict in Yemen marks a major escalation in the regional struggle for influence between Saudi Arabia and Iran, which also back rival sides in Syria's civil war. Arab leaders unveiled plans at a conference Sunday in Egypt to form a joint military intervention force for Yemen, which could raise tensions further.


Critics of the Houthis charge that they are an Iranian proxy. Iran has provided aid to the rebels, but both Tehran and the Houthis deny it has armed them. Iran reiterated those denials Tuesday.


"Claims about the dispatch of weapons from the Islamic Republic of Iran to Yemen are completely fabricated and sheer lies," said the Foreign Ministry's spokeswoman, Marzieh Afkham.


Afkham criticized Saudi-led airstrikes, saying they have caused a high number of casualties and extensive damage.


The Saudi-led coalition on Monday announced it has effectively imposed a naval blockade, days after taking control of the country airspace, to prevent weapons or fighters from getting in or out of Yemen. Also Monday, the coalition repelled a push by the Houthis and their allies, loyal to Yemen's ousted President Ali Abdullah Saleh, toward Aden.


President Abed Rabbo Mansour Hadi had declared Aden a temporary capital after fleeing rebel-controlled Sanaa. Hadi, who was a close U.S. ally against Yemen's powerful al-Qaida affiliate, fled the country last week, but remains Yemen's internationally recognized leader. The U.S. has provided support to the Saudi-led coalition but is not carrying out direct military action.


On Tuesday, coalition warships bombed Aden's airport and Houthi positions on the eastern outskirts of the city, according to Yemeni security officials. It was not immediately clear which coalition countries the ships belong to.


All military and security officials spoke on condition of anonymity because they were not authorized to speak to the media.


By The Associated Press