COPENHAGEN (Reuters) - Denmark will spend about 4 billion crowns ($614 million) on building and procuring 26 navy vessels for patrolling, oil spill response and surveillance of undersea cables, Defence Minister Troels Lund Poulsen said on Tuesday.

Countries bordering the Baltic Sea are on high alert after a number of outages of power cables, telecom links and gas pipelines since Russia's invasion of Ukraine in 2022, including sabotage of the Nord Stream gas pipelines. Russia has denied it was behind the outages.

The NATO military alliance has boosted its presence with frigates, aircraft and naval drones. One concern has been the so-called shadow fleet - vessels used by Russia to move oil, arms and grains around in violation of sanctions.

"The threats we face at sea today are different and far more serious than just a few years ago. In particular, we need to respond to a threatening Russia, while technological development is moving at lightning speed," Poulsen said in a statement.

"With the agreement on the naval plan, we are initiating several urgent procurements that are the first step in enabling Danish maritime defence to counter a wider range of threats."

After more than a decade of drastic cuts in defence spending, Denmark last year allocated 190 billion Danish crowns for its military over a 10-year period.

The Nordic country is primarily aiming to protect submarine cables and pipelines for energy production and transmission, and to boost protection against potential threats to the marine environment in Danish waters from the Russian shadow fleet.

In addition to the 26 vessels, Denmark will acquire drones and sonar systems, which can monitor and identify unwanted underwater activity, the ministry said.

The government said it was aiming for many of the vessels to be built in Denmark, including in cooperation with its NATO allies, but provided no further details.

($1 = 6.5142 Danish crowns)

(Reporting by Louise Rasmussen and Jacob Gronholt-Pedersen, Editing by Timothy Heritage)