It was hoped that the return of the trucks might help ease the tension to some extent in time for talks this weekend, in Ukraine's capital, between visiting German Chancellor Angela Merkel and Ukrainian leaders over how to end the crisis in the ex-Soviet republic.
Western leaders had joined Kiev in calling the Russian convoy -about 220 white-painted trucks loaded with tinned food and bottles of water - an illegal incursion onto Ukraine's soil, and demanded that they be withdrawn as soon as possible.
Journalists at the Donetsk-Izvaryne border crossing, where the convoy rolled into Ukraine on Friday, said more than 100 trucks had passed back into Russia and more could be seen in the distance arriving at the crossing.
But controversy continued after a Ukrainian military spokesman yesterday claimed that the trucks had been loading up production equipment from military plants in Ukraine.
The spokesman, Andriy Lysenko, told reporters that the equipment was taken from the Topaz plant which makes Kolchuga, a type of radar system, and from a factory in Luhansk, eastern Ukraine, which produces firearms magazines.
Earlier, Russian state television had broadcast footage of some of the trucks being unloaded at a distribution depot in the city of Luhansk.
The Russian foreign ministry said the aid reached its intended destination.
The city is held by separatist rebels who are encircled by Ukrainian government forces, and has been cut off from power and water supplies for weeks. International aid agencies have warned of a humanitarian crisis.
Nato said it had reports that Russian troops had been firing artillery at Kiev's forces inside Ukraine - fuelling Western allegations that the Kremlin is behind the conflict in an effort undermine the Western-leaning leadership in Kiev.
"Since mid-August we have multiple reports of the direct involvement of Russian forces, including airborne, air defence and special operations forces in eastern Ukraine," said Nato spokeswoman Oana Lungescu.
Russia denies giving any material help to the rebellion in eastern Ukraine, a mainly Russian-speaking region. It accuses Kiev, with the backing of the West, of waging a war against innocent civilians.
The conflict has dragged Russian-Western relations to their lowest ebb since the Cold War and sparked a round of trade sanctions that are hurting already-fragile economies in Europe and Russia.
Chancellor Merkel landed in Kiev yesterday and was scheduled to meet Ukrainian president Petro Poroshenko and prime minister Arseny Yatseniuk.
In brief remarks at the start of their talks, the German leader said she came to Kiev "in a difficult time which is focused on the unity and territorial integrity of Ukraine".
"I hope that we will be able to discuss bilateral problems and support from Germany as well as the path towards peace, which must be found," she said.
Hours before her plane landed in Kiev, there was heavy artillery bombardment in Donetsk, the main separatist stronghold on the east of Ukraine, near the border with Russia. Reporters saw apartments destroyed and patches of blood, where, according to residents, two civilians were killed.
The unusually intense shelling may be part of a drive by government forces to achieve a breakthrough against the rebels in time for Ukrainian Independence Day, which falls today.
Diplomats say Merkel has two aims for the visit: primarily to show support for Kiev in its standoff with Russia, but also urge Poroshenko to be open to peace proposals when he meets Russian president Vladimir Putin for talks this week.