The blast, which occurred far from where government troops are fighting pro-Russia separatists, came a day after Russia cut gas supplies to Ukraine in a dispute over price and overdue payments.
Ukrainian state gas company Naftogaz said gas flow to Europe was maintained by using a parallel, reserve pipeline. Slovakian pipeline operator Eustream said it saw no fall in pressure in gas pipelines from Ukraine to Europe after the incident.
"Several theories of what happened are being considered, including the main theory of a terrorist act," Interior Minister Arsen Avakov said in a statement.
He said local residents heard two loud claps before the explosion, which occurred in the Poltava region about 200 kilometers (120 miles) east of Kiev, the capital. No injuries were reported.
Emergencies services officials had initially said that the explosion was caused by a loss of pressure in the pipeline.
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