MARANELLO, Italy - Ferrari's Fernando Alonso has responded to Red Bull's Helmut Marko's jibes. In an interview by Red Bull's in-house Red Bulletin magazine, Marko, the team's motor racing chief, spoke of the differences between 2012 champion Sebastian Vettel and runner-up Alonso.Marko said Alonso was caught up in "politics", "funny comments" and "psychological skirmishes", showing he feels the "stress" of the title battle.'I'M FLATTERED'Alonso interpreted the jibes as an acknowledgement by Red Bull that Ferrari would again be the main contender in 2013. He wrote on Twitter: "I enjoy reading that Red Bull still think we will be the strongest rival for 2013! And this even before testing!"I'm flattered." Alonso, however, was not the only driver in Marko's sights. He also reserved some criticism for Vettel's team mate Mark Webber who, according to speculation, could be replaced at the end of 2013.Marke said: "It seems to me that Webber has on average two races per year where he is unbeatable but he can't maintain this form throughout the year."As soon as his prospects start to look good in the World championship he has a little trouble with the pressure that this creates. In comparison with Seb's rising form, it seems to me that Mark's form somehow flattens out."