North Korea has not responded to regularly held calls from South Korea since late last week, Seoul said Tuesday, as speculation grows over further possible provocations by Pyongyang, including a nuclear test."The government expresses strong regret over the North's unilateral and irresponsible attitude," South Korean Unification Minister Kwon Young Se said in a statement."We strongly warn that it will only result in isolation of North Korea itself, making (the country) face more difficult situations."North Korea has not answered phone calls through inter-Korean liaison lines and military hot…READ FULL ARTICLE