COPENHAGEN, Denmark (AP) – Swedish officials do not yet know if an undersea power cable that runs between southern Sweden and Poland was damaged when the Nord Stream gas pipelines some 500 meters (547 yards) away ruptured in what Western officials suspect was an act of sabotage.

“Since the cable is not in service, it can´t be determined if the cable is damaged in some way,” Per Kvarnefalk, a spokesman for Sweden´s public power transmission network operator Svenska kraftnat, said late Thursday. “We will therefore perform tests on the cable using special measurement equipment early next week with the aim to determine if the cable is fully functional.”

Svenska kraftnat partly owns the more than 250-kilometer-long high-voltage cable that transmits electricity through the Baltic Sea.

Following the suspected sabotage this week of the Nord Stream 1 and 2 pipelines that carry Russian natural gas to Europe, there were two leaks off Sweden, including a large one above North Stream 1, and a smaller one above North Stream 2.

The North Stream 2 leak “has diminished, but is still on-going,” the Swedish coast guard said. However, navigational warnings for ships were slightly increased to 7 nautical miles (13 kilometers or 8 miles) from 5 nautical miles from the incident areas, the coast guard said in a statement.

Two leaks also were reported in Denmark’s waters. The Danish and Swedish governments have described the ruptures as the result of “deliberate actions”.

Nordic seismologists recorded explosions preceding the leaks. A first explosion was recorded early Monday southeast of the Danish island of Bornholm. A second, stronger blast northeast of the island that night was equivalent to a magnitude-2.3 earthquake.

NATO warned Thursday it would retaliate for any attacks on the critical infrastructure of its 30 member countries and joined other Western officials in citing sabotage as the likely cause of damage to the natural gas pipelines. Denmark is a NATO member and Sweden is in the process of joining the military alliance.

Russia, which has requested an emergency meeting at the U.N. Security Council to discuss the suspected pipeline sabotage, has said that “it looks like a terror attack, probably conducted on a state level.”

Energy infrastructure security has increased across the Nordic region.

Authorities in Norway, a major oil and gas producer, have reported at least six incidents of drone sightings near offshore installations in the North Sea. It prompted the Petroleum Safety Authority Norway — the Scandinavian country´s oil safety regulator — on Monday to “urge increased vigilance by all operators and vessel owners.” On Wednesday, Norwegian Prime Minister Jonas Gahr Støre said that there was no concrete threat against Norwegian oil and gas off-shore installations.

Danish daily newspaper Ekstra Bladet said a drone was spotted Wednesday near a Danish offshore oil and gas installation in the North Sea.

Sweden stepped up security around its three nuclear power plants.