SINGAPORE - The trading arm for Abu Dhabi National Oil Co (ADNOC) has snapped up several June-loading cargoes of Abu Dhabi's Upper Zakum crude in the spot market, tightening Middle East supply, trade sources said on Wednesday.

ADNOC Trading has bought at least four cargoes of the medium-high sulphur crude from Exxon Mobil Corp, Omani trading firm OQ, Repsol and Aramco Trading at premiums of about $2.20-$2.30 a barrel to Dubai quotes, they said, nearly $1 a barrel higher than the previous month.

ADNOC said it does not comment on such issues. The other oil firms typically do not comment on commercial deals.

The purchases come after ADNOC cut Upper Zakum crude exports sharply in March by diverting supply to its Ruwais refinery which has recently completed an upgrade to process heavier oil into higher quality products. Late last year, ADNOC also cut annual supply of Upper Zakum crude to Asian buyers in 2024 in preparation for the upgraded refinery's crude needs.

Upper Zakum exports in April are hovering around 550,000 barrels per day, similar to the 545,000 bpd seen in March which was the lowest level since November 2017, data from analytics firm Kpler showed.

The drop in supply has limited the number of cargoes of the Abu Dhabi grade that can be delivered during S&P Global Platts' price assessment process for Middle East crude Dubai.

That has led to the delivery of more Murban crude on the Platts window, with PetroChina having sold eight cargoes of the Abu Dhabi light-sour grade so far this month, trade data showed.

(Reporting by Florence Tan; Editing by Himani Sarkar and Louise Heavens)