An oil tanker carrying about one million barrels of Iranian crude arrived in recent days in Venezuelan waters for delivery to the country's largest refinery.

According to a shipping report seen by Reuters on Monday and vessel tracking data, Iran-flagged Suezmax tanker Silvia I, owned and operated by National Iranian Tanker Company, arrived on Sunday to an anchorage area near Venezuela's Amuay port.

The vessel departed in early April from Khor Fakkan, on the Gulf of Oman, and switched off its transponder when navigating near the Cape of Good Hope towards the Atlantic Ocean, according to Refinitiv Eikon monitoring data.

Weeks later, the vessel was seen in satellite pictures close to Venezuela's largest port, the Jose terminal, according to monitoring service TankerTrackers.com.

Iran and Venezuela, which have recently expanded a swap agreement signed last year, have increased the supply of Iranian heavy crude to Venezuela's El Palito refinery and Paraguana Refining Center (CRP).

Despite potential oil market competition, Iranian firms are planning to revamp Venezuela’s largest oil refinery in a deal that would deepen an energy relationship which has become a lifeline for Venezuela’s dilapidated oil industry amid a crisis caused by decades of mismanagement and lack of investments.

However, Iran’s Sharq newspaper reported on Sunday that Iran’s energy dealings with its South American ally have backfired, as Venezuela’s discounted oil exports have increased potentially taking market share from Iran.

Both countries are under American sanctions and try to sell their oil by illicit shipments mostly to China, which has increased its purchases since early 2021. Iranians do not hide that China is buying their oil, but the quantity and price remain a state secret.