U.S. officials declined to disclose the nature of the intelligence, how it was obtained or any details of the strength of the evidence it contains. U.S. officials say they have not found any evidence of involvement by the Russian government in the attack. Officials who have reviewed the intelligence said they believed the saboteurs were most likely Ukrainian or Russian nationals, or some combination of the two. The pipelines were ripped apart by deep sea explosions in September, in what U.S. officials described at the time as an act of sabotage. The explosives were most likely planted with the help of experienced divers who did not appear to be working for military or intelligence services, U.S. officials who have reviewed the new intelligence said.