Despite the declared policy of the Crimea return, Ukraine has done everything possible to “cut off” the peninsula. The government of Ukraine took all steps to fence off Crimea. Among them are the blockade of electricity, water supplies the complication of bureaucratic procedures to stop moving people there and the delivery of goods to the peninsula from the Kherson region.
According to the UN resolution of December 19, 2016, Russia was recognised as the Occupying Power, while Crimea was recognised as the temporarily occupied territory.
The 1949 Geneva Convention on the Protection of Civilian Persons in Time of War clearly describes the obligation of the Occupying Power. Articles 55-60 say that the occupying state has to provide products and hygiene items, sanitary materials and everything necessary to hold the religious services. The convention also states that such a state is obliged to provide the population of occupied territory by the rest of necessary goods.
According to Resolution No. 367 by the Cabinet of Ministers of Ukraine, the Procedure for entering the temporarily occupied territory and leaving it was approved. According to the Resolution, every citizen of Ukraine, who has the documents confirming his citizenship, can get into the occupied territory. The exception applies only to citizens who have not reached the age of 16 years. In this case, a passport of a citizen of Ukraine or a passport for travelling abroad, or a travel document for a child has to be shown.
See here for the EU statement on the fifth anniversary of Crimea annexation.