By CNN's Jill Dougherty, Jamie Crawford and Gregory Wallace
Secretary of State John Kerry's Tuesday call to his Russian counterpart has gone unanswered for nearly a week after North Korea tested a nuclear device.
Kerry called Russian Foreign Minister Sergei Lavrov and top diplomats with the three other countries – South Korea, China and Japan - that had been in negotiations with North Korea over its nuclear program. But Kerry was not connected to Lavrov, who was in Africa for a conference and had "a very overloaded work schedule," according to Russian government spokesman Alexander Lukashevich. He said that the United States did not make additional attempts to call Lavrov.
Russia is an ally of North Korea and a member of the six nations that have held talks over the North Korean nuclear program. The U.S. and North Korea also find themselves on opposite sides of the situation in Syria and have sparred over Russian restrictions on adoptions between the two countries.