US Secretary of State John Kerry finally talked Sunday with Russian Foreign Minister Sergei Lavrov, who had been unavailable for days after the North Korean nuclear test.
President Barack Obama pledged Wednesday a "steadfast" commitment to defend Japan, including preventing nuclear attacks on its ally in the wake of North Korea's third nuclear test.
Iran on Tuesday scorned as a "laughing matter" comments by Israeli Prime Minister Benjamin Netanyahu that Tehran is moving closer to making a nuclear bomb.
With a defiant nuclear test, North Korea has shown it poses an increasingly credible threat but some doubt whether even the notoriously bellicose regime would ever use weapons of mass destruction.
Britain on Tuesday strongly condemned North Korea's announcement that it has staged its most powerful nuclear test yet and called for a "robust response" from the UN Security Council.
North Korea staged an apparent nuclear test Tuesday in a striking act of defiance that, if confirmed, is sure to trigger global condemnation from enemies and allies alike.
Iran faces possible referral to the UN Security Council in early March unless Tehran and the UN atomic agency defy expectations in talks Wednesday and reach a deal on enhanced inspections.
UN leader Ban Ki-moon warned Thursday that a nuclear test by North Korea could blow up hopes of an eventual reconciliation by "tying the hands" of the South's incoming president.
The United States on Wednesday tightened sanctions on Iran to further choke off its oil income, saying it was necessary to increase pressure on Tehran over its suspected nuclear weapons program.
North Korea's expected atomic test will offer a rare chance to gauge where its nuclear programme is headed, with most expert attention focused on what type of device is detonated and how.
North Korea has vowed to carry out a third nuclear test, but scientists and concerned foreign governments may have a tough time verifying the actions of the reclusive state.
Agreeing a venue for the next round of talks between Iran and six world powers on Tehran's nuclear drive was hard enough. Achieving progress will be tougher still.