KIEV, April 18 - Naftogaz Ukrayiny, the national oil and gas company, started custom clearance of imported natural gas on Thursday, the State Custom Service chairman Valeriy Khoroshkovskiy said Friday.

The move comes after law enforcement agencies have started to investigate apparently illegal imports of gas earlier this year during a dispute over gas supplies between Naftogaz and UkrGaz-Energo, a gas trader 25%-owned by Gazprom.