Saudi-led coalition planes have pounded rebels in Yemen for a sixth day, for the first time using ships to bomb the rebel-held airport and outskirts of the port city Aden.

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

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

Meanwhile, Iran said it had sent an aid shipment to Yemen - the first since the Saudi-led airstrikes started.

The aid contained 19 tons of medicine and medical equipment and two tons of food provided by the Iranian Red Crescent.

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 on Sunday in Egypt to form a joint military intervention force for Yemen, which could raise tensions further.

Critics of the Houthis claim they are an Iranian proxy. Iran has provided aid to the rebels, but both Tehran and the Houthis deny it has armed them.

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

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

The Saudi-led coalition said it had repelled a push by the Houthis and their allies, loyal to Yemen's ousted president Ali Abdullah Saleh, toward Aden.