A Russian convoy of 280 trucks sets off from Moscow, en route to eastern Ukraine.
Russian authorities say they're bringing much needed food, water and other aid to the region, where Ukrainian forces are closing in on pro-Russian rebels.
But Kiev believes the convoy is a trojan horse.
And Deputy foreign minister Danylo Lubkivsky says the trucks will not be permitted to enter the country if they're are under escort by Russian military.
(SOUNDBITE) (English) UKRAINIAN DEPUTY FOREIGN MINISTER, DANYLO LUBKIVSKY, SAYING:
"Let me be clear: you don't need tanks and artillery to bring food and medicine for civilians."
This latest stand-off comes in the wake of more fierce fighting around the city of Donetsk, where pro-Ukrainian volunteer fighters exchanged gun fire with rebels, Sunday.
In this battle, six Ukrainians were reported killed and more than 10 were injured.
Despite the rising death toll, Ukraine says the "final stages" of ridding Donetsk