President Vladimir Putin on Monday stood in the driver's cabin of a train for the official opening of a railway bridge that links annexed Crimea to southern Russia.

During his ride starting in Kerch in Crimea in a shortened three-carriage train, Putin also spent time drinking tea with engineers on the 227-billion-ruble ($3.6-billion) project.

The rail bridge, which Putin praised as "magnificent," is 19 kilometres (12 miles) long. The bridge for car traffic opened in May last year when the president drove a truck across it.

The total rail route from the northwestern city of Saint Petersburg to the Crimean port city of Sevastopol covers a distance of 2,500 kilometres (1,550 miles).

Putin said the bridge would restore rail links to Crimea severed in 2014 when Moscow annexed the peninsula, sparking an ongoing separatist conflict in eastern Ukraine that has claimed some 13,000 lives.

The company of Putin's close ally, billionaire businessman Arkady Rotenberg, won the construction contract for the bridge. He sold the company last month.

Russian President Vladimir Putin rides a train connecting the Crimea to mainland Russia
Russian President Vladimir Putin rides a train connecting the Crimea to mainland Russia SPUTNIK / Alexey NIKOLSKY

Putin told workers an anecdote about receiving an emotional call from "your main boss with the simple Russian surname Rotenberg," after the completion of a key stage of the project.

"He called me at night and spoke in such a voice that I asked him 'Have you been drinking?'" said the strongman.

The coverage of the project has been reminiscent of Soviet infrastructure projects, with a newsreader on state-controlled Rossiya 24 television channel calling the opening "without exaggeration historic."

Russia says it is the longest in Europe.

Ukraine was unhappy about both the rail link and Putin's presence at the opening.

President Volodymyr Zelensky's representative office for Crimea said in a statement on Facebook that the rail link and Putin's visit to Crimea were "a gross breach by the Russian side of Ukraine's sovereignty and territorial integrity."

It showed "disregard by the Kremlin of the universally recognised principles and norms of international law," the statement said.