Seoul, Oct 6 : Top South Korean, US and Japanese nuclear envoys strongly denounced North Korea's recent back-to-back missile provocations during their phone talks on Thursday. Kim Gunn, special representative for Korean Peninsula peace and security affairs, and his American counterpart, Sung Kim, voiced "serious concerns" over Pyongyang's test-firing of two short-range ballistic missiles (SRBMs) earlier in the day. The provocation came two days after the launch of an intermediate-range ballistic missile (IRBM) over Japan, Yonhap news agency reported. The two sides called on the North to immediately cease its provocations and condemned the latest salvo of ballistic missiles as a clear violation of multiple U.N. Security Council resolutions, the ministry said in a statement. The South Korean envoy held separate phone talks with his Japanese counterpart Takehiro Funakoshi. The three officials agreed to step up bilateral and trilateral cooperation to respond sternly against the North's nuclear and missile threats, it added. Concerns have also been growing that Pyongyang could conduct another nuclear test in the near future. /IANS