German Chancellor Angela Merkel is due to arrive in Ukraine for talks, a day after calling Russia's decision to send an unauthorised aid convoy there a 'dangerous escalation'.
More than 100 Russian lorries entered eastern Ukraine on Friday without permission from Ukraine's government.
Some of the lorries have now begun crossing back into Russia.
Kiev and Western officials fear the convoy could be part of a general military intervention by Russia.
But Kremlin officials say it is only carrying generators, food and drink.
The lorries had already been waiting at the border for a week. The Russians said they could not wait any longer, owing to the worsening humanitarian situation in eastern Ukraine, which is held by pro-Russian separatists.
The first lorries have now reached the besieged rebel-held city of Luhansk.
Four months of fighting in the region have left more than 2,000 people dead and caused more than 330,000 people to flee their homes.
Entities 0 Name: Ukraine Count: 4 1 Name: Russia Count: 3 2 Name: Kiev Count: 1 3 Name: Luhansk Count: 1 4 Name: Angela Merkel Count: 1 5 Name: Kremlin Count: 1 Related 0 Url: http://ift.tt/1vuN9El Title: Anger over Russian convoy in Ukraine Description: Russia's decision to send more than 100 aid lorries into war-torn eastern Ukraine without permission has been widely condemned in the West. The European Union and the US called for them to be withdrawn as it was a violation of Ukraine's sovereignty, and Nato said it would deepen the crisis.
