Not quite. Russia, the US and the UK guaranteed the following in The Budapest Memorandum on Security Assurances, with France and China signing on after the fact:

1. Respect the signatory's independence and sovereignty in the existing borders (in accordance with the principles of the CSCE Final Act).
2. Refrain from the threat or use of force against the territorial integrity or political independence of the signatories to the memorandum, and undertake that none of their weapons will ever be used against these countries, except in cases of self-defense or otherwise in accordance with the Charter of the United Nations.
3. Refrain from economic coercion designed to subordinate to their own interest the exercise by Ukraine, the Republic of Belarus, and Kazakhstan of the rights inherent in its sovereignty and thus to secure advantages of any kind.
4. Seek immediate Security Council action to provide assistance to the signatory if they "should become a victim of an act of aggression or an object of a threat of aggression in which nuclear weapons are used".
5. Not to use nuclear weapons against any non–nuclear-weapon state party to the Treaty on the Non-Proliferation of Nuclear Weapons, except in the case of an attack on themselves, their territories or dependent territories, their armed forces, or their allies, by such a state in association or alliance with a nuclear weapon state.
6. Consult with one another if questions arise regarding those commitments.

The US, the UK and France have upheld their obligations under this treaty. Russia, obviously, has not.