SOFIA, Jan 13 (Reuters) - These are some of the main stories in Bulgarian newspapers on Monday. Reuters has not verified these stories and does not vouch for their accuracy. - Leader of the nationalist Attack party, Volen Siderov, denied he has hit a police officer at a scuffle at the Varna Airport. Chief Prosecutor has asked for Siderov's immunity to be lifted so he can face criminal charges because of the incident. (24 Chasa, Duma, Presa, Trud, Standart) CAPITAL DAILY - The tender for a constructor for the Bulgarian section of Russia-led South Stream gas pipeline project may be contested in court due to short time before the deadline to file documents, a company source familiar with the situation told the paper. - The European Commission has expressed concerns for the economic viability of the renewable energy installations in Bulgaria after the country imposed a 20 percent charge on its output as of this year. (Capital Daily, Presa, Trud) CAPITAL DAILY - The two main shareholders in Bulgaria's First Investment Bank 5F4.BB , Tseko Minev and Ivailo Mutafchiev, have increased their holdings in the bank to 42.5 percent each, the bank said. The bank will remain floated on the Bulgarian Stock Exchange, Minev said. ((tsvetelia.tsolova@thomsonreuters.com)(+359-2-9399-731)(Reuter s Messaging: tsvetelia.tsolova.thomsonreuters.com@reuters.net)) Keywords: BULGARIA PRESS/