The Pentagon on Friday condemned Russia for sending a 90-truck convoy into Ukraine without permission, calling it a "violation of Ukraine's sovereignty and territorial integrity."

Russia says the trucks are filled with humanitarian aid for Ukraine separatists fighting with Moscow's backing, but Ukraine and its allies, fearing that they contained a trojan horse, had warned that it would not allow the convoy in unless the supplies were handed over to the International Red Cross.

But Russia grew impatient with negotiations and sent in the trucks on Friday morning. Adding to the tension and fears of an invasion directed by Vladimir Putin, NATO officials reported that Russian forces were inside Ukraine and firing artillery at Ukrainian soldiers.

The Pentagon's chief spokesman, Rear Adm. John Kirby, read a statement at the outset of his press briefing Friday calling on Russia to get out of Ukraine.

We strongly condemn this action and any of the actions that Russian forces take that increase tensions in the region. Russia should not send vehicles, persons or cargo of any kind into Ukraine, whether under the guise of humanitarian aid and convoys or any other pretext without Kiev’s express permission. This is a violation of Ukraine’s sovereignty and territorial integrity by Russia. Russia must remove its vehicles and its personnel from the territory of Ukraine immediately. Failure to do so will result in additional costs and isolation."

Kirby did not spell out the "additional costs" would be, but he said the Russian build-up on the border "needs to stop. It just needs to stop."

Kirby was asked about a New York Times report on NATO's comments about the firing of Russian artillery, but he said he had not seen it and wouldn't comment without further information.

The White House echoed Kirby's comments later Friday, with deputy national security adviser Benjamin Rhodes calling the Russian action a "flagrant" violation of Ukraine's sovereignty and warned that Russia would face "consequences" if it did not remove the convoy.

Ukraine immediately responded to Russia's move by calling it a "direct invasion" by Russia, while Russia issued a statement saying, essentially, that it grew tired of waiting for a green light.

All the excuses to delay the delivery of aid to people in the area of a humanitarian catastrophe are exhausted. The Russian side has made a decision to act. Our column with humanitarian cargo starts moving toward Luhansk.”

As the New York Times explained, even if the convoy contained nothing but humanitarian aid, its entry into Ukraine could have tactical military implications, since it would force Ukrainian forces to slow or halt their attacks on the Moscow-aligned rebels.

Spreading the conspicuously large white aid trucks throughout the embattled city could effectively impose a cease-fire, essentially daring the Ukrainians to fire at vehicles that have been sent to provide desperately needed humanitarian assistance.