(Adds PM increasing pipeline protection)
KIEV, June 18 (Reuters) - Ukraine's prime minister ordered security to be reinforced on the country's gas pipeline network on Wednesday to prevent sabotage after the interior minister said an explosion at one pipeline had been caused by a bomb.
Tuesday's explosion on a pipeline in Ukraine's Poltava region that carries Russian gas to the rest of Europe came after Moscow cut supplies to Kiev in a long-standing pricing row.
Though there were no casualties and gas flows were not interrupted, the blast increased tension as Kiev, which is trying to end an uprising by pro-Russian separatists, said it was aimed at discrediting Ukraine as a reliable supplier.
After hearing a report by Interior Minister Arsen Avakov that the explosion had been caused by a bomb placed under a concrete support, Prime Minister Arseny Yatseniuk on Wednesday ordered security to be strengthened at pipeline installations.
"We foresaw some weeks ago that sabotage action would be planned - the aim being to undermine Ukraine's reputation as a reliable transit partner," Yatseniuk said.
"We assume that the explosive device was placed under a concrete block supporting the pipeline and that there were two explosions," Avakov told the government meeting.
"We are studying the circumstances ... external interference is the main cause we are focusing on," he said. (Reporting by Pavel Polityuk; Writing By Richard Balmforth; Editing by Hugh Lawson)