Sweden's coast guard discovered a fourth gas leak on the damaged Nord Stream pipelines, a spokesperson told the Svenska Dagbladet newspaper. 

The European Union suspects sabotage was behind the gas leaks on the subsea Russian pipelines to Europe and has promised a "robust" response to any intentional disruption of its energy infrastructure.

"Two of these four are in Sweden's exclusive economic zone," coast guard spokesperson Jenny Larsson told the paper late on Wednesday. The other two breaches are in the Danish exclusive economic zone.

While neither pipeline was in use at the time of the suspected blasts, they were filled with gas that has been spewing out in the Baltic Sea since Monday's ruptures.

The fourth leak was on the Nord Stream 2 pipeline, in close proximity to a larger hole found on the nearby Nord Stream 1, the Swedish coast guard said. 

This week, Danish authorities reported one hole in each of the two pipeline sections in their waters. 

(Reuters with edits; Cover via CFP)