German Chancellor Angela Merkel on Wednesday appeared to be backing away from a pledge to campaign for the re-election of fellow conservative Nicolas Sarkozy in France, amid unease on both sides of the Rhine and signs that he still trails his Socialist rival by a wide margin.

Merkel's Christian Democrat CDU party said in January she would make joint campaign appearances with Sarkozy, but the party said this week none had been scheduled, raising doubts about whether they will happen at all.

Sarkozy's call on Sunday for tougher controls at Europe's borders sounded alarm bells in Germany even though the French president said he had given Merkel prior notice he would bring it up in his campaign.

Asked on Europe 1 radio whether he still expected to meet Merkel ahead of the election, Sarkozy said without doubt at one moment or another.

I don't think at a rally because the election campaign is a French matter between ourselves, but rather to speak about Europe. It's normal that we speak together, he said.

Merkel endorsed Sarkozy during a joint television interview last month, shortly before the French president formally announced his re-election bid. The two leaders have worked so closely to overcome the euro zone's debt crisis that they have become known by the joint nickname Merkozy.

But German Foreign Minister Guido Westerwelle, a member of the liberal Free Democratic junior partners in Merkel's coalition, told Reuters on Tuesday that Sarkozy was on the wrong track when he called for tougher controls of Europe's borders. The French leader had threatened to pull France out of the EU's Schengen open-border zone unilaterally if he did not get his way.

Sarkozy also raised eyebrows on the other side of the Rhine on Sunday when he said that Europe needed a version of the U.S. Buy American Act which would require governments to favour Europe-made products in public procurement.

Jean-François Copé, the leader of Sarkozy's ruling UMP party, told Reuters that as far as he knew there had never been a plan for Merkel to appear at a Sarkozy rally.

This has not been discussed, at least not at my level, he said.

Merkel has refused to meet Sarkozy's Socialist challenger, Francois Hollande, who has been cold-shouldered by most serving European leaders, partly due to unease about his pledge to renegotiate a new EU fiscal discipline treaty to include more focus on growth.

French Socialists had urged Merkel to show restraint in her support for Sarkozy.

Less than six weeks from the election, Sarkozy has yet to catch up with Hollande in the opinion polls.

On Tuesday, a daily survey by pollster Ifop/Fiducial showed Sarkozy leading his Socialist adversary in the first round for the first time. A poll on Wednesday confirmed this result, with Sarkozy on 28 percent, narrowly ahead of Hollande on 27 percent in voting intentions for the April 22 first round.

But for the May 6 second round, the poll showed Hollande winning comfortably by 54 percent to Sarkozy's 46 percent.