In the city of Melitopol, like many others in the area, red, blue and white Russian flags now fly atop public buildings. Russian security forces patrol the streets and soldiers man checkpoints, inspecting people’s identification documents and looking through the contents of their mobile phones, residents say.

In March, Russian forces burst into the office of Melitopol’s mayor, Ivan Fedorov, put a bag over his head and detained him. Moscow named a local pro-Russian politician to replace him. Mr. Fedorov was later released in a prisoner swap and is now in Ukrainian-held territory.

Russian occupation authorities have said they would seek to make the Russian ruble legal tender and say they will reopen schools teaching a Russian curriculum. Mr. Fedorov said Melitopol is now connected to Russia’s internet via a fiber-optic cable from Crimea. There also are new Russian cellphone-service towers…

In some places, Russian forces have also hoisted the flag of the Soviet Union on government buildings and moved to replace statues of Lenin dismantled after 2014.