An explosion at the giant Tengiz oil field in Kazakhstan killed two workers and injured three, Kazakhstan police said on July 6.

The explosion occurred when testing a pipeline at the oil field, the TASS news agency reported.

It was not immediately clear if production was impacted.

Police in Kazakhstan said they had opened an investigation into the incident.

Tengiz is Kazakhstan’s largest oil field, operated by the country’s top oil venture Tengizchevroil, in which Chevron Corp. holds a 50% stake.

The country is a major oil producer, pumping around 1.6 million bbl/d in line with an agreement with OPEC.