An Iranian foreign ministry statement said that Tehran "dismisses Bahrain's baseless, false claims".
"It is better for Bahraini officials to establish serious dialogue with their people to put an end to the crisis in the country instead of raising worn-out claims... and suppressing the legitimate demands of their people,"
Bahrain's interior ministry said that four Bahraini men, aged 23 to 27, had been arrested for "plotting" and "remotely bombing" the pipeline outside the capital Manama.
Two of the four had received "intensive training at the Iranian Revolutionary Guard camps with the help of the leading fugitive terrorists living in Iran," it said.
Three others remain at large, it added.
Bahrain accused all seven of belonging to the "February 14 Coalition" -- a reference to a protest movement that emerged in 2011 against the Al-Khalifa dynasty, which has ruled the kingdom for more than two centuries.
Protests by Bahrain's Shiite majority against the kingdom's Sunni rulers have continued to rock the small but strategic Gulf state as authorities clamp down on dissent.
Bahrain frequently accuses opposition figures of links to Iran, which denies supporting any bid to overthrow the government.