GENEVA (AFP) - The UN refugee agency said it had launched a huge operation Wednesday to bring desperately needed aid to half a million Iraqis driven from their homes by jihadist rebels.

"It's the largest single aid push we have mounted in more than a decade," UNHCR chief Antonio Guterres said in a statement.

The first Boeing 747 of the 10-day operation flew into the Iraqi Kurdish city of Erbil from Jordan carrying 100 tonnes of aid including tents, plastic sheets, kitchen sets, and jerry cans.

It was the first consignment in an operation that aims at bringing a total of 2,410 tonnes of aid by the start of September.

Three other flights were due to leave Jordan on Thursday, Friday and Saturday carrying 100 tonnes each.

Aid was also on its way by road and sea, with 175 trucks bringing tents, blankets, plastic tarpaulins, and household items across borders from Turkey, Jordan and Iran from UNHCR warehouses in the region and Europe.

"This is a massive logistics operation to bring in relief supplies by air, land, and sea to help the hundreds of thousands of desperate people who have fled suddenly with nothing but their lives, and are now struggling to survive in harsh conditions," said Mr Guterres.

The goal, the agency said, is to help almost 500,000 displaced people in the region, many of whom are crammed into unfinished buildings, living in parks or by the roadside.

Jihadists from the Islamic State group which had already occupied parts of Syria launched an offensive in Iraq in June and rapidly seized much of its Sunni heartland.

They have declared a "caliphate" in a region straddling the Iraq-Syria border, and have taken Iraq to the brink of breakup.

Many of those fleeing have found a haven in Iraq's Kurdistan region, whose fighters have provided a bulwark against the jihadists.

The UNHCR said Kurdistan was hosting over 600,000 internally displaced civilians, among them more than 200,000 people who have fled the flashpoint Sinjar area since the beginning of this month.

They include members of Iraq's Christian and Yazidi religious minorities, whom the jihadists have given a "convert or die" option.

Across Iraq, an estimated 1.2 million people have been displaced so far this year, including over 500,000 who fled fighting in the Anbar region which erupted in January.