The Russian government is set to construct a rail and road bridge connecting Crimea and southern Russia, which is anticipated to cost around $1.4bn.
The move comes after Russia President Vladimir Putin signed a treaty to incorporate Crimea into the country, which is yet to be approved by Russian Constitutional Court and ratified by both houses of parliament.
NATO Secretary General Anders Fogn Rasmussen said: "There can be no justification to continue on this course of action that can only deepen Russia’s international isolation. Crimea’s annexation is illegal and illegitimate and NATO Allies will not recognise it."
The proposed project forms a part of the agreement between Russia and Ukraine in December 2013.
The rail and road bridge will be constructed on the 4.5km-wide Kerch strait, which connects the Black Sea and the Sea of Azov.
This will enable the movement of people and cargoes directly to Crimea without entering mainland Ukraine.
Federal road agency Rosavtodor has been appointed to oversee the development of the rail and road project.
The project is expected to be completed over the next three-and-a-half years.
Russia is also evaluating the possibility of constructing a rail tunnel under Kerch Strait.
Russia Transport Minister Maxim Sokolov said: "We will carry out all these parallel processes as quickly as possible in order to start the construction of the bridge as soon as possible."