"Allies express deep concern over the destabilising actions Russia continues to carry out across the Euro-Atlantic area, including on alliance territory, and stand in full solidarity with the Czech Republic," NATO's 30 allies said in a statement.
The dispute, which has led to tit-for-tat diplomatic expulsions in Prague and Moscow, is the sharpest between the two countries since the end of the Communist era in 1989 and comes at a time of acute tensions in Russia's relations with the West.
(Reporting by Robin Emmott, editing by Marine Strauss, Reuters)