Spain has called for tighter scrutiny of oil transfers involving tankers at sea as the number of unregulated ships hit by sanctions grows and raises pollution risks, a U.N. agency session heard this week.

Hundreds of extra “ghost” tankers have joined this opaque parallel trade over the past few years as a result of rising Iranian oil exports as well as restrictions imposed on Russian energy sales over the war in Ukraine.

The number of incidents last year including groundings, collisions and near misses involving these ships reached the highest in years, a Reuters investigation showed.

Spain raised the issue this week at the legal committee of the United Nations’ shipping agency, the International Maritime Organization (IMO), and submitted a resolution to “address the consequences and concerns” over the increase in such operations, a Spanish transport ministry source told Reuters on Friday.

Spain’s Mediterranean and Atlantic coastlines have become hubs for shipping activity including the transfer of oil known as ship-to-ship (STS) operations.

Madrid, which has already tightened its rules for STS transfers around its coastline, has called for flag states to step up scrutiny and enforcement of such activity, the source added.

“We express our willingness to support any international initiative aimed at resolving this problem and, to this end, we are urging at the international level initiatives against such STS operations outside our waters,” the source said.

A paper submitted to the IMO committee by Australia, the United States and Canada said illicit transfers “undermine the rules-based international order”.

The IMO committee said the shadow tankers “posed a real and high risk of incident”, particularly when engaged in STS transfers. The tactics used to obscure ship identities including turning off AIS ship tracking transponders “undermined the spirit of the regulation” as prescribed by the MARPOL maritime convention, minutes from the session showed.

[reuters]