Feb 8 (Reuters) - Russia's foreign ministry said on Wednesday the United States had questions to answer over its role in explosions on the undersea Nord Stream gas pipelines last year. Commenting on a report published earlier on Wednesday that said the United States was involved in the explosions, Russia's Foreign Ministry spokeswoman Maria Zakharova called on the White House to comment on the "facts" that had been presented. Construction of Nord Stream 2, designed to double the amount of gas Russia could send directly to Germany under the sea, was completed in September 2021, but was never put into operation after Berlin shelved certification just days before Moscow sent its troops into Ukraine in February