Is there a foreign submarine in Swedish waters?

The Swedish military has been searching coastal waters near Stockholm, the capital, for a vessel it thinks is a foreign submarine.

"It could be a submarine or a smaller submarine. It could be a diver using some form of moped-like underwater vehicle, and it could be divers who don't have any business on our territory. That's where I think you have the span of what could be foreign underwater activity," said Rear Adm. Anders Grenstad of the Swedish Royal Navy.

Several sightings of a mysterious vehicle, including some captured in amateur photographs, have engaged the nation’s attention and begun a full-throttle hunt.

Not since the Cold War has Sweden, a neutral nation, seen such a mobilization.  Back then Sweden used depth charges to counter frequent Soviet incursions along its coast. The Swedish government has not specifically accused Russia of any territorial violations. Still, the Russian Ministry of Defense said in a statement, "There have been no irregular situations and, even less so, accidents involving Russian naval vessels."

The region has been on edge recently. In September, Sweden said two Russian warplanes entered its airspace. And on several occasions this week NATO scrambled fighter jets to intercept Russian aircraft flying over member states' territory on the Baltic Sea.

Sweden is not a member of NATO and has been cutting its defense spending for years — leading to criticism that it is not prepared for rising tensions with or provocations from Russia.

Sweden's newly minted Prime Minister Stefan Lofven has announced his government will increase spending on defense in its new budget. All this comes as Russia is already at odds with the West, flexing its muscle and intimidating neighbors.

The conflict between Kiev and restive eastern Ukraine has been bloody, and Moscow is accused of fomenting the conflict by supplying soldiers, weapons and money.  International condemnation and a sanctions program aimed at Vladimir Putin and his friends have done little to change the dynamic there and failed to reverse the Russian annexation of Ukraine’s Crimean Peninsula.

If there is a foreign vessel in Swedish waters, what could it be?

If it is a foreign vessel, how will that affect Swedish and Baltic defense policies?

What signs point to Russian involvement?

We consulted a panel of experts for the Inside Story.