Russian President Vladimir Putin has warned the West not to cross a "red line" with Russia and condemned what he called a coup plot against Belarus. The warning came in his annual state of the nation address, amid heightened tension with the West over Ukraine and jailed Putin critic Alexei Navalny."The use of unjust sanctions is growing into something more dangerous: a coup attempt in Belarus," he said.He backs Belarusian President Alexander Lukashenko, who faces huge opposition. On 17 April the Belarusian authorities announced that they had foiled a US-backed plot to assassinate President Lukashenko. Russia's Federal Security Service (FSB) said it had detained two Belarusians allegedly involved in the plot. The coup claim was dismissed by the exiled Belarusian opposition leader Svetlana Tikhanovskaya as a "provocation". There have been massive demonstrations in support of her since Mr Lukashenko claimed re-election last year, in a vote widely condemned as rigged. Thousands of protesters were beaten up by police and detained. Warning to West President Putin said Russia wanted good relations with all countries, but there were constant attempts by Western powers to "pick on" Russia. "We don't want to burn bridges, but if somebody interprets our good intentions as weakness our reaction will be asymmetrical, rapid and harsh." He said: "We'll decide for ourselves in each case where the red line is". Tensions have been building over Ukraine, as reports say Russia has moved more than 100,000 troops close to disputed areas. A large part of that force is in Crimea, the peninsula which Russia annexed from Ukraine in March 2014. A senior Ukrainian officer, Gen Serhiy Nayev, estimated the total force to be 103,200 last week. Russia backs the separatists holding a swathe of eastern Ukraine, and its manoeuvres have fuelled fears of a new Russian military intervention. n his speech Mr Putin said that "the West didn't think about Belarus or Ukraine, when the Maidan events were going on there". Mass protests in Kyiv's Maidan Square led to pro-Russian President Viktor Yanukovych fleeing to Russia in February 2014. "The organisers of any provocations against Russia will regret [their actions] in a way they never have before," Mr Putin warned. Last week the US government accused the Kremlin of "malign activity" and expelled 10 Russian diplomats. Russia responded tit-for-tat. Similar hostile exchanges of diplomats took place between Russia and both the Czech Republic and Poland.