Russia has reportedly informed the United States that it will boycott the 2016 Nuclear Security Summit in Chicago.
The move, if confirmed, would be a blow to efforts first initiated by US President Barack Obama to reduce the threat of nuclear terrorism.
Reports are suggesting the tensions between the US and Russia over Ukraine are one of the main stumbling blocks.
Moscow has already been absent from last week's initial planning session in Washington.
White House spokesman Josh Earnest. "The United States regrets Russia's decision not to participate in last week's preparatory meeting for the 2016 Nuclear Security Summit. As far as the United States is concerned, the door remains open to Russia joining future meetings like this."
The nuclear summits were initiated in 2010 to prevent terrorists from getting their hands on weapons-grade nuclear material.
