SINGAPORE/LONDON - SAUDI Arabia has cut oil supply to some major customers with immediate effect, industry sources said on Tuesday, easing doubts about whether the world's top exporter will comply quickly with OPEC cuts.

The kingdom has told major oil companies that it will restrict the volume they can load this month by limiting operational tolerance, one of the sources who is familiar with Saudi crude sales told Reuters.

Another source with a major customer of state oil firm Saudi Aramco also confirmed that he saw evidence that Riyadh had cut supplies in Nov. Neither source was able to give an estimate on how much exports had been cut in total.