Sweden PM says 'clear evidence' foreign submarine entered its waters last month It's impossible ... to confirm any nationality. But we can confirm the fact that it has been there," Supreme Commander Sverker Goranson said at a joint news conference with Mr Lofven and Defense Minister Peter Hultqvist. Mr Goranson said the military obtained evidence of the intrusion with its own sensors, but declined to give details. Mr Lofven noted that Sweden's coastline is as long as the U.S. East Coast, making it difficult to monitor, but promised to strengthen the country's ability to find and identify intruders. A photo allegedly showing an object travelling southwards at a speed of one knot inside Swedish waters (EPA) "Let me say this, loud and clear, to those who are responsible: It is completely unacceptable," Mr Lofven said. Sweden built up an anti-submarine force after a Soviet sub with nuclear weapons ran aground off its southern shores in 1981, but started dismantling the force as part of deep cuts in defense spending after the Cold War ended. Anti-submarine helicopters were phased out in 2008 and replacements are not expected until 2018.