Armenia's ambassador to Russia said on Monday that Turkey had sent around 4,000 fighters from northern Syria to Azerbaijan amid fighting over the breakaway region of Nagorno-Karabakh, the Interfax news agency reported. The ambassador said the fighters were taking part in fighting in Nagorno-Karabakh, a region inside Azerbaijan that is run by ethnic Armenians, the RIA news agency reported. Armenian and Azeri forces exchanged fierce fire for a second day on Monday over the region, with both sides accusing each other of using heavy artillery. Turkey is a close ally of Azerbaijan.