International groups are delivering aid to people in Yemen under "extraordinarily difficult and dangerous" conditions, UN aid chief Stephen O'Brien said in his first briefing to the Security Council.

The impoverished Arab state is divided among pro-government troops supported by Saudi Arabia, Houthi rebels and al Qaeda militants. More than 6,000 people have died in the fighting since March 2015.

The warring parties are "contributing to the reduction of humanitarian access," according to O'Brien.

Last week, the Saudi-led coalition diverted a World Food Program ship headed to Yemen, and Saudi Arabia also denied entry to the regional humanitarian coordinator in January, O'Brien said.

Millions need food and medical help

Houthi rebels have also been inconsistent when it comes to granting access to territories under their control. They have allowed aid workers to some areas but denied humanitarian missions to Ibb, Taiz and Saada. Movement in al Qaeda-held areas is also "extremely challenging," according to the UN official.

"I remind all parties of their obligations under international humanitarian law to facilitate humanitarian access to all areas of Yemen," O'Brien said, pointing out the "staggering needs" of the Yemeni population.

At least 7.6 million people in the country are "severely food insecure," and 10.6 million need "urgent health support," he said in the Security Council briefing.

Riyadh's warning slows aid

O'Brien also criticized a recent note from Saudi Arabia advising humanitarian workers to "move any offices and staff they may have in regions where the Houthi militia and their supporters are active and in areas where there are military operations."

Observers claimed that this warning might be construed as a threat to aid organizations helping the Saudi opponents. Riyadh has rejected this view of its message.

The Saudi note "impacted the humanitarian community's planning, causing delays to important missions over the past two weeks," O'Brien said.

The UN is set to launch a humanitarian appeal of $1.8 billion (1.6 billion euros) to fund aid operations in Yemen on Thursday.

dj/sms (AP, dpa, Reuters)