0159 GMT January 18, 2019
Support for their Social Democrats (SPD) coalition partner meanwhile hit a record low, according to a poll published hours before senior members of both the CDU and the SPD were due to discuss the parties' future courses in closed-door meetings, Reuters wrote.
Merkel announced last week that she would step down as CDU party leader in December, ending an era of nearly two decades in which she shifted the party gradually from the right to the center.
Her decision followed two regional votes in which Merkel's center-right bloc and the left-leaning SPD suffered their worst election results in decades while the ecologist Greens and the far-right Alternative for Germany (AfD) gained support.
Health Minister Jens Spahn, one of the three contenders to replace Merkel as party leader, said the CDU had watered down its profile by becoming too centrist in the past years.
"Parties must differ from another again more strongly," Spahn told Welt am Sonntag newspaper. "The way we view people and society is fundamentally different from the one of the Social Democrats," he added.
Spahn is one of the fiercest critics of Merkel's decision in 2015 to welcome more than a million refugees, mainly Muslims from war zones in the Middle East.
Spahn ruled out a coalition with the anti-immigration AfD, writing on Twitter that the CDU could not work together with a party he called anti-American and which he said idolises Russian autocrats. He also accused the AfD of wanting to roll back European integration and tolerating anti-Semitism within its ranks.
CDU deputy chair Armin Laschet warned against moving the CDU more to the right. "I'm convinced that such a policy shift would be wrong," Laschet told Sueddeutsche Zeitung daily. The CDU should stick to its centrist course, he added.
The candidate most likely to stand for a continuation of Merkel's course is CDU party secretary general Annegret Kramp-Karrenbauer who is expected to comment on her candidacy in the coming days.