A surface-to-air missile launcher secretly crossed over from the Russian border and into war-torn eastern Ukraine early morning, The Sunday Times reported.
The radar-controlled missile system known by the Russians as the Buk-M1 and by NATO forces as the SA-11 Gadfly is bristled with four missiles capable of shooting down enemy aircraft flying at up to 72,000ft.
But 15 hours after slipping across the Russian border, the weapon is believed instead to have destroyed Malaysia Airlines flight MH17 as it flew at about 33,000 ft above the war zone, the report said.
All 298 people on board more than 80 of them children were killed.
Using intercepted mobile phone calls and satellite imagery, senior Ukrainian officials say they can accurately reconstruct the sequence of events that led to the tragedy.
Their claims, disclosed to the British daily, are vigorously denied by the Russia and pro-Moscow rebels.
According to the Ukrainian account, the launcher crossed the porous border with Russia near the village of Sukhodolsk.
The launcher, carried on the back of a low-loading lorry, reached the city of Donetsk, the rebels' stronghold and command centre.
Telephone conversations posted on the internet by the Ukrainian Security Service (SBU), purport to reveal militants discussing the delivery of the weapon.
The recordings follow photographs and video that emerged on Friday that appear to show a launcher with a missile in vertical launch mode beside a supermarket in the Torez district, east of Donetsk.
At about 4pm the Buk, commanded by a junior rebel officer known by the nom de guerre "Miner", stopped in the nearby village of Pervomayski.
At 4:10 pm a Russian operator reported the aircraft to Miner who, mistaking the Boeing 777 for a Ukrainian AN-26 transporter, allegedly gave the fateful order to fire.
The rebels were initially jubilant, thinking they had successfully downed yet another Ukrainian aircraft.
Four days earlier they had used a surface-to-air missile to bring down an AN-26, killing two military personnel.
Shortly after the airliner was destroyed, Igor Girkin, the leader of the Donetsk People's Army, posted on his Russian social media page a message claiming his men had shot down a Ukrainian cargo plane.
The chilling message was quickly removed after news broke of MH17's downing.