This file photo shows the SN Olivia tanker.
The Iraqi state oil firm has put on its blacklist three tankers involved in shipping crude from the semi-autonomous northern region of Kurdistan, which has been bypassing the central government in Baghdad to export oil.
In a recent letter sent to oil market participants and seen by Reuters, the State Organization for Marketing of Oil (SOMO) said that it would not permit the ships Maran Centaurus, Four Smile and SN Olivia to enter Iraqi ports or export Kurdish crude.
The development came one day after the Iraqi government reached an agreement with Iraq's Kurdistan Regional Government (KRG) to start talks on oil revenue sharing. 
The negotiations will focus on the production and distribution of crude from the Kurdish region and the nearby Kirkuk area, the office of Iraqi Prime Minister Haider al-Abadi said in a statement.
Earlier this month, Baghdad also resumed shipping crude from the Kirkuk fields to Kurdistan.
Last week, however, Baghdad warned that it could divert the Kirkuk crude to Iran by truck instead of sending it to Kurdistan via pipeline if the talks with the KRG broke down.
The Iraqi government has been locked in an oil dispute with the KRG. Since mid-2015, Kurdistan has been exporting crude independently, accusing Baghdad of having failed to respect an oil revenue sharing deal and transfer enough money to Erbil.
Baghdad, in turn, has accused Erbil of not exporting enough crude under the deal.
Kurdistan exports some 500,000 barrels per day (bpd) of its crude from the Turkish Mediterranean port of Ceyhan.
Falling oil prices have severely hit the Kurdish region, which like the capital, Baghdad, heavily relies on oil income to provide the majority of its funds.
This is while the northern and western parts of Iraq have been plagued by gruesome violence ever since Daesh terrorists mounted an offensive in June 2014.