PRAGUE, Dec 17 (Reuters) - Former Slovak prime minister Robert Fico is facing charges of incitement, police said on Friday, after he organised a protest that fell foul of lockdown rules as the country battles a rise in COVID-19 cases. In a statement sent by his opposition Smer party, Fico said his detention on Thursday - ahead of a planned protest against the government and president - was unconstitutional. He was quoted by local media as calling his detention a government attack on an opposition leader. Police said on their Facebook page that Fico had been released from custody but faced charges of incitement, without giving further details. The case will now go to prosecutors. Slovakia has faced a jump in coronavirus cases since November, although the daily infection rate has slowed in the past week and the government has eased some COVID measures for vaccinated people. Public gatherings are still limited as the government seeks to slow the spread of the virus and ease pressure on hospitals. Fico resigned as prime minister in 2018 amid mass protests over perceived public corruption in the wake of the murder of a journalist and now sits in the opposition in parliament.