Ukraine’s ambassador to the United Nations asked the U.S. and other key members of the 15-nation security council for help after Russia said it would send armed forces into neighboring Ukraine, Reuters reported Saturday.

“The situation continues to deteriorate,” Yuriy Sergeyev told the council, adding that Russian forces represent “an act of aggression against the state of Ukraine … posing a serious threat to our sovereignty and territorial integrity.”

Ukraine’s U.N. Ambassador Yuriy Sergeyev speaks to the media following a U.N. Security Council meeting on his country’s crisis, Saturday, March 1, 2014, at United Nations headquarters. (Image source: AP/John Minchillo)

Sergeyev said Russia’s actions violate a 1994 agreement safeguarding Ukraine; it’s known as the Budapest Memorandum, and all five members of the permanent security council — the U.S., the United Kingdom, France, China, and Russia — agreed to it.

Sergeyev is now asking the four nations besides Russia to make good on their promises.

“Now what we are doing is we are addressing for other guarantors (of Ukraine’s sovereignty) to perform their guarantees,” Sergeyev told reporters Reuters noted.

Russian Ambassador Vitaly Churkin dismissed Sergeyev’s criticisms and described the council meeting on the Ukrainian crisis as a “game without rules.”

Russia’s U.N. Ambassador Vitaly Churkin speaks during a U.N. Security Council meeting on the Ukraine, Saturday, March 1, 2014, at United Nations headquarters. (Image source: AP/John Minchillo)

Besides Russia’s veto powers on the Security Council, the other complicating factors center on what form any assistance from the U.S. and the other three nations would take.

U.S. Ambassador to the United Nations Samantha Power called for the “immediate deployment” to Ukraine of international monitors from the United Nations and the Organization for the Security and Cooperation in Europe (OSCE), Reuters said.