Activists circulated on social media images and videos showing the moment Russian forces and tanks entered, in the early hours of Tuesday morning, the outskirts of Donetsk, the capital of one of the two separatist regions in eastern Ukraine, after Russian President Vladimir Putin recognized them as two independent states.

On Monday evening, the Russian president ordered the Ministry of Defense to send "Russian peacekeeping forces to the two pro-Moscow separatist regions in eastern Ukraine, which he recognized as independent."

On Monday, Russia officially recognized the regions of "Donetsk" and "Luhansk" as two independent states separate from Ukraine.

The two decrees signed by Putin order the Russian Ministry of Defense that "the Russian armed forces undertake the peacekeeping mission on the territories of the Donetsk and Luhansk People's Republics."

The United States took a wait-and-see stance on Monday regarding President Putin's order for Russian forces to deploy within the separatist regions of Ukraine, noting that the diplomatic route is possible as long as Russian tanks have not yet moved.

A U.S. official told reporters: "We will assess what Russia has done," revealing that Russian forces have been covertly present in the separatist regions for eight years.