Sweden’s Coast Guard said Thursday it has discovered a fourth leak in the Nord Stream pipelines built to carry Russian gas under the Baltic Sea, as NATO formally blamed sabotage for underwater explosions that led to Monday’s rupture. NATO did not blame Russia for the attack, though leaders of several NATO member nations have blamed the Kremlin, without citing evidence. Meanwhile, Russian officials suggested the U.S. or one of its allies is to blame. The disaster is now thought to be the largest fossil gas leak in history. The U.S. Geological Survey estimates it added a tenth of a percent of estimated annual global methane emissions to the atmosphere.