North Korea's defence ministry accused the United States and South Korea of ramping up reconnaissance activities around the inter-Korean border, warning that it will act if its sovereignty and security is violated, state media KCNA said on Sunday. North Korea's vice defence minister Kim Gang Il said the U.S. had flown at least 16 of its RC-135 and U-2S strategic reconnaissance planes and RQ-4B drone over the Korean peninsula between May 13 and 24. He also accused South Korea's navy and coast guard of stoking military tension by stepping up patrol activities and increasingly breaching the maritime border.