"There were no flight clearances granted to our flights today…We expected to have two flights going and those are on hold for now," said UN spokesman Farhan Haq on Monday.
He added that UN officials are currently trying to persuade the Saudis to permit aid delivery to Yemen, where some seven million people are suffering from severe malnutrition, Press TV reported.
On Sunday, the kingdom announced that it is shutting down all Yemen’s air, sea, and land border, after Yemen targeted an international airport near the Saudi capital.
The Yemeni army on Sunday, said that it had targeted Saudi Arabia’s King Khalid International Airport in Riyadh with a long distance Borkan H2 ballistic missile.
Riyadh also put some 40 high-ranking Ansarullah movement officials on a terrorists' list.
Saudi Arabia has been incessantly pounding Yemen since March 2015 in an attempt to crush the popular Houthi Ansarullah movement and reinstate former president Abd Rabbuh Mansur Hadi, who is a staunch ally of the Riyadh regime.
More than 12,000 people have been killed since the onset of the campaign more than two and a half years ago. Much of the Arabian Peninsula country's infrastructure, including hospitals, schools and factories, has been reduced to rubble due to the war.
Another 2,100 people have died of cholera since April as hospitals struggle to secure basic supplies across the country.
Last week, the international medical charity Doctors Without Borders warned that millions of Yemenis face a "desperate" health situation on top of the ravages of war as Saudi Arabia continues its military aggression against its impoverished neighbor.