Russia's Prime Minister Dmitry Medvedev has called for international talks, to secure energy and water supplies for Crimea, after Western powers slapped the country with strict sanctions following the referendum.
Medvedev said in a ministerial meeting that "this issue needs to be decided through international negotiations."
"We need to choose the best way to supply the peninsula."
Crimea siphons 80% of its electricity supplies from Ukraine and 85% of its water from beleaguered country.
On 21 March, Russia's upper house of parliament unanimously approved a treaty to annex Ukraine's Crimea region, and finalised the legal process.
President Putin signed a law amending the Russian constitution to reflect the transition of moving Crimea into its sovereignty.
"I ask lawmakers of both chambers to work actively and do everything we can, to make the transition process not only painless, but also beneficial for all Russia and the people of Crimea," Putin said, following the signing of the law.
Meanwhile, Russian troops have stormed and taken control of a Ukrainian naval base using stun grenades in the port city of Feodosia.
"The mission's mandate reflects the new political and legal realities and does not apply to Crimea and Sevastopol, which became a part of Russia," said the Russian Foreign Ministry in a statement.
"Russia hopes that the objective and impartial work of the international observers will help to overcome the internal Ukrainian crisis, stop rampant nationalist banditry, eradicate ultra-radical tendencies."