UPDATE 1-S.Africa May crude imports from Iran down slightly m/m

* May Iran imports at 285,524 T vs 286,072 T in April

* Total crude imports at 1.95 mln T (Adds details, background)

JOHANNESBURG, June 29 (Reuters) - South Africa's crude oil imports from Iran fell marginally in May to 285,524 tonnes from 286,072 tonnes the previous month, customs data showed on Friday, as Pretoria continued to cut shipments to avoid U.S. sanctions.

Africa's biggest economy used to import a quarter of its crude from Iran, but has come under Western pressure to cut the shipments as part of sanctions designed to halt Tehran's suspected pursuit of nuclear weapons.

South Africa imported a total of 1.95 million tonnes of crude in May. The main suppliers were Saudi Arabia, Angola and Nigeria at 572,635 tonnes, 530,140 tonnes and 412,732 tonnes, respectively.

Even though the United States granted South Africa an exemption from financial sanctions after the cuts in Iranian imports, Pretoria may still face problems because of sanctions from the European Union, which does not provide any waivers.

Talks with Brussels on the matter are ongoing, the department of energy said earlier in June.

The United States will also be watching to see if South Africa continues to keep imports from Iran low.

When comparing monthly averages over a six-months period, South Africa imported around 266,762 tonnes of crude from Iran per month in the December to May period, compared with 466,503 tonnes in the preceeding six months.

Some South African refineries are designed to treat Iranian-type crude only, and analysts say refiners will be hard-pressed to replace those supplies with other products.

Any disruption to crude imports could hit fuel supplies in South Africa, which has suffered shortages in the last year because of strikes and refinery problems.

Refiners in South Africa include Shell, BP, Total, Chevron, petrochemicals group Sasol , and Engen, which is majority-owned by Malaysian state oil group Petronas. ($1 = 8.4314 South African rand) (Reporting by Agnieszka Flak; Editing by Ed Stoddard)