Aid workers say they were stopped by security officials at Addis Ababa Bole International Airport on Thursday afternoon, ahead of their flight to Tigray region in northern Ethiopia.
The workers allege they were also harassed and subjected to extra checks when they arrived to board a United Nations humanitarian flight bound for Mekelle, the troubled region's capital.
A UN official, who declined to be named due to fear of reprisal, told Nation.Africa that the aid workers were harassed by State security officials.
"Security officials ordered them not to carry medicine and cash more than 10,000 birr (about $230)," the official said.
"In protest of the harassment, some WFP (World Food Programme) and UN officials even refused to board the flight," the official adds.
"Putting so much pressure on aid organisations could potentially affect effective and timely aid operations to Tigray" the UN official warned, adding:
"Time is critical in saving the lives of people who might be starving to death within minutes or hours."
Ethiopian officials were not immediately available for comment by press time.
Despite the incident at Bole Airport, the WFP humanitarian plane later took off and landed at Mekelle's Alula Aba Nega International Airport later in the day.
“WFP and our fellow emergency responders on the ground in Mekelle are all enormously relieved to see this United Nations Humanitarian Air Service (UNHAS) flight arrive today, bringing in colleagues who are all essential in our collective efforts to scale up the humanitarian response and for WFP to reach 2.1 million people with life-saving food assistance,” said Michael Dunford, WFP's regional director for Eastern Africa in a statement.
Today's flight was the first UNHAS passenger flight, which is managed by WFP.
According to the UN agency, it was the first passenger flight to the region since Ethiopia halted commercial flights on June 24.
The plane carried more than 30 employees from multiple humanitarian organisations working to deliver urgently needed assistance to conflict-affected communities across Tigray.
Last week, Addis Ababa accused aid groups operating in Tigray of attempting to smuggle arms to the Tigray People's Liberation Front (TPLF) and threatened to suspend the humanitarian activities of some charities.
State minister for foreign affairs, Mr Redwan Hussein, at the time said that aid groups were "playing a destructive role."
"Instead of coordinating aid, they are widely engaged in coordinating, from a distance, campaigns of propaganda to harass and defame the Ethiopian government," he alleged.
Today's incident at Bole Airport is just the latest manifestation of the Ethiopian government's suspicion of aid groups including the WFP, Médecins Sans Frontières (MSDF) and other humanitarian agencies working in the country.
Earlier this month, Ethiopia said that it had allowed humanitarian flights to Tigray but said it will conduct serious inspections upon arrival and departure of workers.
After the Ethiopian army withdrew from Tigray, the region doesn't have access to communications, electricity, water and banking.
The last remaining aid delivery corridor was land transport, which had been halted after TPLF fighters launched offensives in the neighbouring Afar region.