After months of tension, Ukraine says it's finally happened: Russia has invaded.

Russia, however, flatly denies it. "This information doesn’t correspond with reality,” a spokesman for Putin, Dmitry Peskov, said Wednesday.

There's not really a middle ground here. Russia's invasion has either begun, or it hasn't. So what evidence is there in support of Ukraine's claims? Here are five big pieces of evidence:

200 Russian trucks entered and left eastern Ukraine

Last week, 200 white trucks said to be carrying humanitarian aid headed to eastern Ukraine from Russia. Russia called it an aid convoy but Ukraine indicated that it would allow the trucks in only if they were accompanied by teams from the International Committee of the Red Cross (ICRC).

However, despite a wait at the border, the trucks eventually entered Ukraine on Friday -- without permission from the government in Kiev or ICRC chaperones. Only a small portion of the trucks were searched by Ukrainian officials, and there was deep suspicion that the trucks could be being used to rearm separatist rebels or bring in Russian hardware in some way.

The trucks left Ukraine just one day after they arrived.

Russian soldiers were captured inside Ukraine

On Tuesday evening, Ukraine brought out nine of 10 men who it said were Russian paratroopers captured in Donetsk region. In a video the Ukrainian government released of the men, one soldier explained he was a “contractor” in the Russian army and he was in Ukraine “for training.” The men were said to be "detained" and not prisoners.

Russia has denied that the men were part of any invasion and said they must have entered Ukraine by mistake. "The soldiers really did participate in a patrol of a section of the Russian-Ukrainian border, crossed it by accident on an unmarked section, and as far as we understand showed no resistance to the armed forces of Ukraine when they were detained," a military source was quoted as saying by the Russian press.

While things like that have happened in the past, this would be remarkably bad timing.

A Russian tank may have been caught on video inside Ukraine

The BBC reports that a modern T-72 variant tank, currently in use by the Russian military, has been spotted in Ukraine. It is the second tank in the video above.

While older, Soviet-era Russian tanks have been seen multiple times before in Ukraine, this appeared to be the first time that a tank currently operated by the Russian army -- and, importantly, not exported in large numbers -- had been seen in Ukraine, Joseph Dempsey, an analyst with the International Institute for Strategic Studies, told the BBC.

Separatist leaders had publicly bragged about the Russian military entering Ukraine

In the video above, published on YouTube earlier this month, Alexander Zakharchenko, the self-declared prime minister of the separatists' Donetsk People’s Republic, spoke of the Russian hardware entering Ukraine.

“At present, moving along the path of this corridor . . . there are 150 items of combat hardware, 30 of which are tanks,” Zakharchenko says in the video, according to a translation from the Financial Times. He said that “1,200 individuals who underwent four months of training in the Russian Federation" were also on their way.

Zakharchenko's remarks were later denied by Russia.

NATO satellite imagery appears to show Russian troops inside Ukraine

On Thursday, NATO released a number of satellite images from Digital Globe that purport to show Russian artillery, vehicles and troops inside Ukraine. For example, the picture above appears to show Russian artillery setting up in Krasnodon, a rebel-held town in eastern Ukraine.

"The satellite images released today provide additional evidence that Russian combat soldiers, equipped with sophisticated heavy weaponry, are operating inside Ukraine’s sovereign territory,” Dutch Brig. Gen. Nico Tak, director of the Comprehensive Crisis and Operations Management Center (CCOMC), said in a statement.

Ukraine says it is now actively fighting Russian troops inside its borders

On Thursday, Ukraine's military announced it had fought two armored columns of Russian forces near Novoazovsk. The Ukrainian troops were overwhelmed by tanks and armored fighting vehicles, a spokesman said, and the town was now controlled by Russian troops.

“Our border servicemen and guardsmen retreated as they did not have heavy equipment,” Col. Andriy Lysenko said in a statement. Ukrainian President Petro Poroshenko announced that he had canceled a trip due to the news, explaining that "Russian troops have actually been brought into Ukraine."