The monitors were alerted to the seizure of the building by local media, who reported that the Odessa office of the Communist Party was occupied by the Right Sector last Friday.
The SMM said it went to the office a day after the reports emerged to confirm them. The monitors said they observed four camouflage-clad Right Sector activists with baseball bats and truncheons outside the office. They were told there were five to six additional activists inside.
On Monday, the SMM again tried to enter the Communist office. "The SMM saw Ukrainian and Pravyi Sektor [the Right Sector] flags still outside the premises and met the head of the Pravyi Sektor, who denied the SMM access to the building," the report says.
The city of Odessa made headlines in spring 2014 when a blaze at the Trade Unions House claimed the lives of almost 50 anti-Kiev protesters as they fled a mob of football fans and Right Sector members.
Russia has repeatedly tried to draw international attention to the rise of far-right groups in Ukraine. Radical nationalist organizations, including the Right Sector, played an important role in the ousting of President Viktor Yanukovych in February 2014, and are currently fighting against Ukrainian pro-independence militias in the southeast.