Ethiopia's government has used the country's flagship commercial airline to shuttle weapons to and from neighboring Eritrea during the civil war in Ethiopia's Tigray region, a CNN investigation has found. Cargo documents and manifests seen by CNN, as well as eyewitness accounts and photographic evidence, confirm that arms were transported between Addis Ababa's international airport and airports in the Eritrean cities of Asmara and Massawa on board multiple Ethiopian Airlines planes in November 2020 during the first few weeks of the Tigray conflict. It's the first time this weapons trade between the former foes has been documented during the war. Experts said the flights would constitute a violation of international aviation law, which forbids the smuggling of arms for military use on civil aircraft. Atrocities committed during the conflict also appear to violate the terms of a trade program that provides lucrative access to the United States market and which Ethiopian Airlines has benefited greatly from. Ethiopian Airlines is a state-owned economic powerhouse that generates billions of dollars a year carrying passengers to hubs across the African continent and all over the world, and it is also a member of the Star Alliance, a group of some of the world's top aviation companies. The airline previously issued two denials about transporting weapons. Responding to CNN's latest investigation, Ethiopian Airlines said it "strictly complies with all national, regional and International aviation related regulations" and that "to the best of its knowledge and its records, it has not transported any war armament in any of its routes by any of its Aircraft." The governments of Ethiopia and Eritrea did not respond to CNN's requests for comment. Long-simmering tensions between Ethiopia's government and the ruling party in the Tigray region exploded on November 4, when Ethiopia accused the Tigray People's Liberation Front of attacking a federal army base. Abiy Ahmed, Ethiopia's Nobel Peace Prize-winning prime minister, ordered a military offensive to oust the TPLF from power. Government forces and regional militias poured into Tigray, joined on the front lines by troops from Eritrea. Thousands of people are estimated to have died in the conflict, which by many accounts bears the hallmarks of genocide and ethnic cleansing. While all sides have been accused of committing grave human rights abuses during Tigray's war, previous CNN investigations established that Eritrean soldiers have been behind some of the worst atrocities, including sexual violence and mass killings. Eritrea has denied wrongdoing by its soldiers and only admitted to having troops in Tigray this spring. Documents obtained by CNN indicate that flights carrying weapons between Ethiopia and Eritrea began at least as early as a few days after the outset of the Tigray conflict. On at least six occasions -- from November 9 to November 28 -- Ethiopian Airlines billed Ethiopia's ministry of defense tens of thousands of dollars for military items including guns and ammunition to be shipped to Eritrea, records seen by CNN show. On November 9, five days after Abiy ordered a military offensive in Tigray, records show an Ethiopian Airlines flight transported guns and ammunitions from Addis Ababa to Asmara, Eritrea's capital. The shipments came at a time of increased military activity; security sources in the region told CNN the Eritreans needed re-supply for the fight in Tigray. As planes went back and forth between the two countries, massacres of Tigrayans in the city of Axum and the village of Dengelat by Eritrean troops took place on November 19 and November 30 respectively. Some current and former Ethiopian Airlines employees, who spoke on condition of anonymity for fear of repercussions, said the flights continued past this date but that the majority of arms trips to Eritrea were in November. Both cargo and passenger planes were used in the operation, though CNN has no evidence that commercial passengers were on any of the flights carrying weapons. Many of these flights do not appear on popular online flight tracking platforms such as Flightradar24. When they do, the destination in Eritrea is often not visible and the flight path vanishes once the plane crosses the border from Ethiopia. The employees told CNN the staff could manually turn off the ADS-B signal on board to prevent the flights being publicly tracked. The flights were often assigned the same flight numbers, primarily ET3312, ET3313 and ET3314, with 'ET' being the code for Ethiopian Airlines. Ethiopian Airlines workers described witnessing other airline employees loading and unloading arms and military vehicles on flights directed to Asmara. A few even claimed they helped load the weapons on the planes themselves. All spoke of being ethnically profiled for being Tigrayan. CNN has seen the Ethiopian Airlines' ID cards of these employees and confirmed their identities. One former employee told CNN they were instructed at Addis Ababa's Bole International Airport to load guns and four military vehicles onto an Ethiopian Airlines cargo plane that was due to fly to Belgium but was sent instead to Eritrea. The former employee warned soldiers that the vehicles were carrying far more gas than was allowed under international air transport rules, but said they were overruled after a direct call from an army commander. The flight, loaded with both weapons and flowers, traveled to Eritrea, then returned to Addis before flying on to Brussels the following day, the employee said. CNN cross-referenced this testimony with Flightradar24 and found the record of an Ethiopian Airlines aircraft returning from the direction of Eritrea and flying to Brussels the next day, but could not independently verify it was the same flight referred to by the employee. Days later, the employee said they were temporarily suspended from work. They believe they were suspended for being Tigrayan but also for the incident with the soldiers. The employee fled Ethiopia in March. Ethiopian Airlines told CNN in its statement that no employees had been suspended or terminated due to their ethnic background.