On Sunday, it seemed that the trucks would be inspected Monday, with the Red Cross tweeting: "Border and customs officials from Russia and Ukraine agree to inspect first group of Russian convoy trucks shortly," adding, "We will observe."
But by Monday, that plan was put on hold.
The Red Cross has reportedly sought security assurances from both Ukraine and Russia.
Ukrainian National Security and Defense Council spokesman Andriy Lysenko blamed Russia for the delay, telling reporters Monday that:
"Due to the absence of any agreement between terrorist organizations and Red Cross representatives on safety guarantees for the convoy with humanitarian cargo border and customs clearance procedures were not carried out. Detailed inspection of the contents of the Russian humanitarian convoy has not started."
Lysenko pointed to an incident on Sunday that underlined the need for security assurances. Sixteen vehicles "allegedly from a humanitarian convoy arrived at the Donetsk checkpoint in Russia and parked near the checkpoint." Then, he said, armed militants in eight cars and three buses crossed from eastern Ukraine into Russian territory in an attempt to forcibly bring the aid convoy across the border.
"Ukrainian border guards take up defensive positions to repel the attack," Lysenko said, describing the tense standoff. "After negotiations with Russian border guards, the terrorists retreated deep into the territory of Ukraine."
A senior Red Cross representative will arrive in Moscow on Tuesday to discuss the status of the Russian humanitarian convoy, Russia's ITAR-TASS news site reported.