Sweden has found a fourth leak on one of two major undersea pipelines which EU leaders believe are the subject of sabotage. Western leaders say the gas leaks in the Nord Stream 1 and 2 pipelines in the Baltic Sea earlier this week were "deliberate and irresponsible." The two pipelines running between Russia and Germany aren't operational, but they reportedly contain up to 778-million cubic metres of natural gas, a source of methane. The Danish Energy Agency says the pipelines contained 778-million cubic metres of natural gas in total - the equivalent of 32 percent of Danish annual CO2 emissions. Some experts don't believe the latest leak is a separate attack, as the BBC's Damien McGuinness reports. Corin Dann spoke to Imperial College London's department of chemical engineering research associate Jasmin Cooper.