In an apparent show of force, a fleet of Russian warships and aircraft arrived in the Cuban capital of Havana on Wednesday.

Small groups of fishermen and curious onlookers lined the Malecon seafront boulevard in light rain to welcome the ships as they passed the 400-year-old Morro castle at the harbor's entrance.

The first to arrive was a fuel ship, the "Akademik Pashin" and a tug, the "Nikolay Chiker," while a Russian navy frigate and nuclear-powered submarine waited offshore and were expected to enter the harbor by mid-morning.

The frigate and submarine, part of the group of four Russian vessels that arrived off Cuba on Wednesday, had conducted missile drills in the Atlantic Ocean en route to the island, Russia's Defense Ministry said the previous day.

Cuba said last week that the visit was standard practice by naval vessels from countries friendly to Havana. The communist-run government's Foreign Ministry said the ships carried no nuclear weapons, something echoed by U.S. officials.

"We have been monitoring the ships' paths closely," a U.S. official told Reuters on condition of anonymity late Tuesday. "At no point have the ships or submarine posed a direct threat to the United States."

Havana is just 160 kilometers (100 miles) from Key West, Florida, home to a U.S. Naval Air Station. And the timing of the visit – as the Biden administration ponders how far to go in helping defend Ukraine against Russia – suggests more than "standard practice," said William Leogrande, a professor at American University.

"The visiting Russian warships are Putin's way of reminding Biden that Moscow can challenge Washington in its own sphere of influence," Leogrande said.

The stopover also coincides with Cuba's worst social and economic crisis in decades, with shortages of everything from food, medicine and fuel and growing discontent on the streets.