UPDATE 2-Suncor says leak from Colorado oil refinery contained

* Leak from firm's refinery hits South Platte River

* Firm says leak has been contained, source not identified

* Refinery warned that stricter safety measures needed

By David Sheppard and Joshua Schneyer

Nov 30 (Reuters) - Suncor Energy said on Wednesday it has contained a leak of an oily substance near its Commerce City refinery in Colorado that was running into Sand Creek, which joins a river that supplies Denver with water.

The Canadian energy firm said it had not yet identified the source of the leak, but acknowledged it was likely coming from its 93,000 barrel-per-day (bpd) refinery in the area. It said plant operations were unaffected.

The leak comes a month after Colorado's Department of Public Health warned Suncor that it needed to take stricter measures to mitigate contamination that an investigation found was coming from the site and could threaten local water supplies.

Neither Suncor nor the Environmental Protection Agency (EPA) gave an estimate on how big the leak was, which the EPA said appeared to be a petroleum product.

A spokeswoman for the company, based in Calgary, said it was not clear if there had been a leak from one of the plant's pipelines, as reported by some media.