Nissan has admitted that it has uncovered falsified data from car exhaust emissions tests at most of its Japanese factories.

The firm did not disclose how many cars were involved, but said emissions and fuel economy tests had "deviated from the prescribed testing environment".

The carmaker added that inspection reports had been "based on altered measurement values".

Nissan pledged there would be a "full and comprehensive investigation".

It added that "appropriate measures" would be taken to stop any future recurrence.

Nissan has not revealed how many cars were involved in the altering of data, or if it involved vehicles manufactured outside Japan.

The company said it had rechecked "reliable" data and confirmed that all vehicles except the GT-R sports car conformed to Japanese safety standards. It did not explain why the GT-R had been excluded.