The International Organization for Migration said Tuesday it had temporarily suspended evacuations of foreigners from Yemen because of security hurdles posed by "all parties to the conflict".
Spokesman Joel Millman said the IOM had been forced to suspend the operation that began on April 12 "until further notice" due to "escalating difficulties faced in undertaking flight operations in recent days".
The IOM said it had flown more than 400 foreign nationals out of the war-torn country since April 12.
The organisation had hoped to operate several flights out of the conflict-ravaged country daily, but had only managed three flights since the evacuations began, Millman told reporters.
"We did our last flight Sunday the 19th, and took out almost 140 stranded migrants," he said, adding that they had been flown to Addis Ababa in Ethiopia.
The two previous flights on April 12 and 14 had taken some 300 people to the Sudanese capital Khartoum, he said.
A coalition of Sunni Arab nations led by Saudi Arabia launched air strikes last month against Yemen's Shiite-backed rebels, vowing to restore the authority of President Abedrabbo Mansour Hadi, who fled the rebel advance to Riyadh.
The World Health Organization said Tuesday that Yemen health facilities had registered 944 deaths and 3,487 people injured in the conflict as of April 17, but warned that the toll was likely higher since many people are not reaching hospitals for treatment.
"We call on all parties to the conflict to provide timely clearance for flights, cease demands to add passengers onto humanitarian evacuation flights on the basis of criteria other than the genuine vulnerability of populations of concern as well as guarantee unhindered and safe access for IOM staff in Yemen," a statement said.
Millman stressed that the main obstacle was not the aerial bombing, but instead the violence raging on the ground.
"We have to talk to the coalition members, (but) for the most part, getting enough time has not been the issue, or avoiding the bombardment. It's just the climate of violence around the airport," he said.
The IOM said the UN Security Council had adopted a resolution calling on all the belligerents in Yemen to help in the evacuation of foreigners but this was not being respected.
Millman said there were still hundreds of thousands of foreigners in the country.
Some 16,000 foreign nationals had turned to IOM alone requesting evacuation.
But Millman pointed out that there are known to be around 250,000 Somalis and 100,000 Ethiopians living in Yemen.
While many of them may not want to be evacuated, the number of foreigners who wish to leave is "potentially a huge population," he said.