DONETSK, Ukraine, Oct 16 (Reuters) - About 200 protesters in separatist-controlled Donetsk confronted monitors from Europe"s main security and rights watchdog on Saturday to demand the release of a pro-Russian officer captured by the Ukrainian military. The monitoring mission of the Organization for Security and Cooperation on Europe has previously faced protests organized by pro-Russian rebels, but this time protesters for the first time appeared to block the entrance to the hotel where they are based. A Reuters reporter saw four men in surgical masks standing close to each other at the doorsteps leading to the gate of the Park Inn, where the monitors live and have an office. They appeared to be unarmed. Two dozen tents were set up on a lawn in front of the hotel and a protester cut firewood with a chainsaw. Several OSCE monitors were seen on a terrace right outside the hotel but did not leave it or come closer to the protesters. One filmed the crowd on a smartphone. Russian-backed rebels claim the Ukrainian military captured their officer, Andrei Kosyak, near the front line on Wednesday while he was part of a joint committee that oversees the ceasefire. The Ukrainian defence ministry said that Kosyak, who it said was a Russian citizen, belonged to a group of Russian servicemen who had carried out an undercover reconnaissance mission. Russia denies that it has forces in eastern Ukraine, which was taken over by Russian-backed separatists in 2014, in a conflict that Kyiv says killed 14,000 people. The protesters demanded that the OSCE help to get the officer released. "OSCE, fulfil your mandate," one of banners held by protesters read. The OSCE mission, which has monitored the conflict since its start, said in a statement on Saturday it was ready to facilitate dialogue on the ground between the sides. "This readiness has already been communicated to the sides," it said. It did not comment on the protest at the hotel.