MOSCOW — Russia’s President Vladimir Putin today called on pro-Russian separatists to release Ukrainian soldiers who have been surrounded by the rebels in eastern Ukraine.

Putin’s statement came several hours after Ukraine accused Russia of entering its territory with tanks, artillery and troops, and Western powers accused Moscow of lying about its role and dangerously escalating the conflict.

NATO said at least 1,000 Russian troops are in Ukraine and later released what it said were satellite photos of Russian self-propelled artillery units moving last week.

Russian Foreign Minister Sergey Lavrov dismissed the accusations of an invasion in a televised news conference today, saying Moscow “has not been presented with any facts” proving that it had happened.

For the second day, Russian markets reacted nervously to the escalation of the conflict in Ukraine with the Russian ruble diving to the all-time low of 37.10 rubles against the U.S. dollar in early morning trading, but recovered later to 36.90 rubles.

Markets dropped on Thursday on reports of Russia’s apparent invasion in Ukraine, sparking investors’ fears of further economic sanctions directed at Moscow. The ruble lost 1.4 percent against the dollar and the MICEX benchmark shed 1.6 percent.

“I’m calling on insurgents to open a humanitarian corridor for Ukrainian troops who were surrounded in order to avoid senseless deaths,” Putin said in the statement published on the Kremlin’s web-site in the early hours on Friday.