(Adds German prosecutor's comments in paragraphs 5-6)

By Bernhard Winkler

LUDWIGSHAFEN, Germany, Feb 7 (Reuters) - Turkish Prime Minister Tayyip Erdogan called for calm on Thursday when he visited the site of a fire in a western German city which killed nine people of Turkish origin and heightened community tension.

The cause of Sunday's blaze in an apartment block in Ludwigshafen is not known but speculation is rife in the local Turkish community and in Turkish media that it was a racially motivated arson attack.

The fire revived memories of a firebombing by Germans in 1993 in Solingen which killed five Turks and drew international condemnation. One person in the crowd listening to Erdogan brandished a placard recalling the Solingen attack.

"Let us all help to strengthen the friendship between Germany and Turkey," Erdogan said at the burnt-out building. He urged the press to stop fuelling tension.

Lother Liebig, a German state prosecutor, said the investigation into the fire could last weeks. Police were not ruling anything out but preliminary inquiries had not found any traces of fire-stoking materials that would suggest foul play.

The probe was focusing on the building's electrical wiring and there was evidence power was being illegally piped off in the basement, Liebig said. Two young girls who reported seeing arsonists were being questioned further, he added.

Turkish newspapers have reported that a family who lost members in the blaze had been threatened by neo-Nazis.

Turkey's Aksam newspaper carried a story on Thursday which recalled German media and officials descending on Antalya in southern Turkey during the trial of Marco Weiss, a German teenager charged with sexually abusing a 13-year-old British girl.

He was detained in Turkey for about eight months and German Chancellor Angela Merkel became involved in the case.

"Officials mobilised for Marco's release but now the same officials say 'We don't understand Turkey's reaction'," the paper said.

TURKEY JOINS POLICE PROBE

A Turkish team has flown to Germany to help the police investigation and Erdogan told a news conference at Ankara airport before leaving for Germany that Turkey expected a full investigation of the causes of the blaze.

"We are in contact with the German authorities to have the incident clarified ... If it is a case of arson, the culprits must be punished," he said.

German Interior Minister Wolfgang Schaeuble, who says there is no reason for Turks to doubt the competence of German authorities, also condemned some Turkish reporting.

"When media stir things up like this, one should not be surprised there are consequences," he told RTL television.

In a sign of the sensitivity of the issue, German public broadcaster ARD decided to postpone the broadcasting of a police drama set in the Turkish-German community in Ludwigshafen which was due to be shown on Sunday.

"There is a danger that the production would have been misunderstood," said ARD director Peter Boudgoust.

Germany is home to at least 2.5 million people of Turkish descent, many of whom live in separate communities. The German government, aware of growing social problems, has vowed to improve integration.

Hours before Erdogan's arrival, police in Ludwigshafen received a threat to attack a building close to the site of the blaze. After checking the building with sniffer dogs, they gave the all clear.

Erdogan is due to meet Merkel on Friday. (Additional reporting by Gareth Jones in Ankara) (Writing by Madeline Chambers, editing by Tim Pearce)

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