* General says retaliatory measures needed
* NATO says moves in Eastern Europe are purely defensive (Adds NATO comment)
MOSCOW May 23 (Reuters) - Russia will retaliate against increased NATO activity near its border, its top general said on Friday, in the latest sign of tensions with the western alliance over Ukraine.
Since Russia annexed Ukraine's Crimea region in March, NATO has moved to reassure its nervous eastern European allies by stepping up military exercises in the region and temporarily deploying additional ships and planes.
"NATO's military groupings in the Baltic states, Poland and Romania are being built up, as well as the military presence of the bloc in the Baltic, Mediterranean and Black Sea," General Valery Gerasimov, the chief of general staff of the Russian armed forces, told a defence conference in Moscow.
"The intensity, the operational and combat readiness of the alliance's troops is being increased near the Russian border. In these circumstances ... we have to take retaliatory measures."
A NATO spokeswoman said the measures were purely defensive.
Russia has always opposed NATO enlargement in eastern Europe, a process that has expanded the alliance's membership to 28 nations including three former Soviet republics and a handful of other ex-Warsaw Pact states once dominated by Moscow. President Vladimir Putin said last month that his annexation of Crimea was partly influenced by NATO enlargement.
Russia has concentrated tens of thousands of troops across the border from eastern Ukraine, where pro-Russian separatists have declared independence from Kiev, but its deputy defence minister said on Friday they would all be pulled back within days.
Asked to comment on Gerasimov's remarks, NATO spokeswoman Oana Lungescu said NATO had taken appropriate measures to enhance its members' collective security "in light of the new security situation created by Russia's illegal aggression against Ukraine".
"These are defensive measures, fully in line with our international obligations. NATO's core job is to defend allies and this is what we are doing," she said.
She said NATO urged Russia to respect its international commitments, pull back all its forces from close to the Ukraine border and stop destabilising Ukraine.
The crisis in Ukraine, which holds a presidential election on Sunday, has left ties between Russia and the Western alliance at their lowest ebb since the Cold War.
NATO last month suspended all practical cooperation with Russia to protest its absorption of Crimea.
But despite tension over Ukraine, NATO Secretary General Anders Fogh Rasmussen said earlier this month that the bloc did not expect to base large numbers of new combat troops in eastern Europe. (Reporting by Thomas Grove, additional reporting by Adrian Croft in Brussels; Writing by Alissa de Carbonnel; Editing by Mark Trevelyan)