Russian President Vladimir Putin said Monday that, in conjunction with the Red Cross and with approval of the Ukrainian government, Russia is sending an aid convoy to eastern Ukraine, despite warnings from NATO that humanitarian help could act as a pretext for invasion.

Last week, the Ukrainian military closed in on the pro-Russian rebel-held towns of Donetsk and Luhansk, the target of the proposed humanitarian aid. The area has seen intense fighting in recent weeks which has caused hundreds of thousands of residents to flee. 

Although the Ukrainian presidential press service said that President Barack Obama agreed to the plan in a phone call with Ukrainian President Petro Poroshenko, NATO says there is "a high probability" of Russian military intervention. 

"We see the Russians developing the narrative and the pretext for such an operation under the guise of a humanitarian operation, and we see a military build-up that could be used to conduct such illegal military operations in Ukraine," NATO Secretary-General Anders Fogh Rasmussen said to Reuters. Russia has reportedly assembled 45,000 troops by the border. 

As a partner in the convoy, European Commission President Jose Manuel Barroso "warned against any unilateral military actions in Ukraine, under any pretext, including humanitarian," in a statement following a call with Moscow. 

All of this falls on the heels of another day of fighting in which officials said 106 inmates in a high-security prison near Donetsk escaped after rockets struck the complex, further adding to the chaos.