Russia’s State Duma, the lower house of parliament, has overwhelmingly approved a treaty to annex Crimea from Ukraine, taking the Black Sea peninsula a step closer to joining the Russian Federation.

The Federation Council or upper house will hold a similar vote on Friday, completing the ratification process of a treaty that was signed by President Vladimir Putin on Tuesday.

An integration period of some nine-months will follow.

The annexation has caused outrage with Kyiv, Washington and Brussels, where the move is considered illegal and unacceptable.