BERLIN, March 15 (Reuters) - Germany’s liberal Free Democrats, emboldened by gains in a regional vote on Sunday, would not be drawn on Monday on their potential as kingmaker in a national government after federal elections in September. Germany holds federal elections in September and, with Chancellor Angela Merkel not seeking re-election after 16 years in office, her party suffered historic defeats in twin regional votes on Sunday, already missing the “Merkel bonus” she has brought it with four consecutive national election victories. In the southwestern automotive hub of Baden-Wuerttemberg, the business-friendly Free Democrats (FDP) increased their share of the vote to 10.5% from 8.3% at the previous election in 2016. The gains opened the way for a potential regional alliance of the ecologist Greens, SPD and FDP, dubbed a ‘traffic light’ coalition after the parties’ colours. Before Sunday’s vote, the Greens ruled in coalition with Merkel’s Christian Democrats. In neighbouring Rhineland-Palatinate, which also voted on Sunday, a traffic light coalition was already in power before the election, and could govern again. “Coalition speculation is too early,” FDP leader Christian Lindner told a news conference in Berlin, referring to September’s federal election. The party’s secretary general, Volker Wissing, said the outcome of the regional elections could not simply be transferred to the federal level. “Of course we want to govern. But now we have to say: state politics and federal politics cannot be compared one-to-one,” Wissing, who is also FDP state chairman and economy minister in Rhineland-Palatinate, told broadcaster ARD. “And it must also be clear to everyone: With the FDP, there will be no shift to the left in Germany,” he added. Merkel’s conservative bloc of her Christian Democrats (CDU) and their CSU Bavarian allies now rule at federal level in a ‘grand coalition’ with the left-leaning Social Democrats (SPD). The CDU/CSU bloc would prefer to rule at a national level with the FDP, but opinion polls show it lacks the support for such an alliance now. The fractured electoral landscape could open up scenarios such as a CDU/CSU tie-up with the Greens, a ‘traffic light’ coalition, or an alliance of CDU/CSU, Greens and FDP. Polls do not show enough support for a left-wing combination of Social Democrats, Greens and far-left Linke. (Writing by Paul Carrel Editing by Peter Graff)