Skuld is warning shipowners that ship-to-ship transfers in Malaysia, Africa and the Caribbean could unwittingly expose them to sanctions risk.

The Norwegian protection and indemnity club said in a note on Tuesday that owners should be cognisant of the tactics counterparties might use to move cargoes subject to US sanctions amid growing oil exports from Iran and Venezuela.

"Many [ship-to-ship] transfers are legitimate; however, suspicious circumstances such as operations at night and in high-risk areas, anchoring or drifting near sanctioned countries, and missing AIS data should raise immediate concern," Skuld said.

The club said ships are increasingly using fraudulent documents related to cargo and inventing ship identities, including fake vessel registrations and International Maritime Organization numbers, to get around the US blacklist.

Skuld recommended doing extra due diligence if the transfer is happening in problematic areas. Shipowners should also include clauses in contracts stating no parties are subject to sanctions and keep an eye out for gaps in a ship's automatic identification system history — a practice the US has long been pushing for.

According to data analytics firm Kpler, in 2021 Iran has exported more oil each month than the year prior, peaking in March when it exported 43.7m barrels per day, an improvement from the 37.3m barrel per day three-month average.

Venezuela's monthly output has only shown moderate year-over-year growth since May, but in recent weeks its four-week average has jumped from 2m barrels per day to 2.6m barrels per day, Kpler data shows.

The US has slowed down its "maximum pressure" campaign against Iran as the two hope to renew a 2015 agreement that would see sanctions lifted. But many key organisations in the Iranian economy remain on the US blacklist, blocking their access to US financial markets and potentially exposing whoever does business with them the same.

The sanctions have also kept the tanker market oversupplied with tonnage, according to Euronav and Frontline.

Chief executives of both companies have complained older ships reputable charterers would pass on find work in sanctioned trades, keeping them at work rather than the breakers.