NATO Secretary General Anders Fogh Rasmussen on Tuesday warned Russia that attempting to take over more of Ukraine would be a "historic mistake" and called for the country to pull back its forces.
"We call on Russia to pull back the tens of thousands of troops it has massed on Ukraine's borders, engage in a genuine dialogue with the Ukrainian authorities, and respect its international commitments."
Tensions are rising in Ukraine after pro-Russian protesters this week took over government buildings in the eastern part of the country. Russia has massed troops along the Ukrainian border, raising fears that Vladimir Putin intends to seize more of the country.
Rasmussen also called for increased readiness in the multinational NATO Responce Force.
"We should place parts of it at very high readiness," Rasmussen said.
He also called for an end to defense cuts in Europe.
"Over the past years, some of our European Allies have cut their defence spending by as much as 40 percent, while other countries, like Russia, are increasing theirs by 30 percent," he said. "The reality is that Europeans have disarmed too much and for too long."