International law restricts Denmark from enforcing EU sanctions against Russian vessels transiting the Danish Straits, but environmental and safety regulations allow limited inspections and detentions, posing challenges and opportunities for sanction enforcement and maritime safety.

The Danish Straits (the Sound, the Great Belt and the Little Belt) are crucial maritime routes linking the Baltic Sea to the Atlantic Ocean, through which significant Russian maritime trade passes. The EU has imposed extensive sanctions on Russia, including prohibitions on transporting certain Russian goods through European waters, including the Danish Straits. However, international law, notably the 1857 Copenhagen Treaty and UNCLOS, guarantees free transit passage of foreign merchant vessels through these Straits, which limits Denmark's ability to enforce these sanctions on Russian-owned or operated vessels. Denmark cannot prohibit transit passage unless vessels violate international marine pollution prevention laws or other applicable safety regulations. Recent incidents involving Russian oil tankers with dubious safety records and insurance coverage highlight environmental risks. Danish authorities can inspect such vessels and may detain those lacking proper insurance under the 1992 Civil Liability Convention. While enforcement of Russian sanctions in the Danish Straits is constrained by international law, the Danish government shows intent to enhance oversight of tankers to mitigate environmental hazards and indirectly curb sanctioned Russian activities in the region.