Ukraine's interior minister Arsen Avakov lashed out at Moscow's move as a "provocation by the cynical aggressor" and reiterated Kiev's insistence that "no humanitarian convoy of (Russian President Vladimir) Putin's will be allowed to cross the territory."
Earlier, it said the trucks would be stopped at the border, and the aid unloaded and transported into conflict-torn eastern Ukraine with the help of the International Committee of the Red Cross (ICRC).
The mission has sparked fears the four-month conflict, which has already left over 1,500 dead and plunged relations between Moscow and the West to a post-Cold War nadir, could be about to escalate even further. Western powers say Russia might use the operation as a "Trojan horse" to sneak in troops or weapons for pro-Moscow insurgents, who have been losing ground against government troops in eastern Ukraine. Russia said suggestions that it could use a humanitarian aid convoy to Ukraine as a cover for invasion were absurd. In a statement released on Wednesday the country's foreign ministry criticised Australia for voicing such fears.
"They continue to voice the absurd claim that the humanitarian convoy to help the civilian population of southeast Ukraine could be used as a pretext for Russian 'military intervention'," the statement said.
Moscow insists it has coordinated the mission with the ICRC and that the convoy does not include military personnel. But the ICRC has denied it is involved and told AFP news agency they had not been able to check what was inside the convoy. A journalist from Russian tabloid Komsomolskaya Pravda travelling with the convoy wrote on Twitter on Wednesday morning that the lorries had halted as they waited for "political decisions" to be taken. Other Russian journalists with the convoy said it was due to arrive at the border by Wednesday evening.
There were concerns in Kiev that the vehicles, officially bound for a government-controlled border checkpoint, could take a different route to the east across a rebel-held stretch of the border.