Recep Tayyip Erdogan, Turkey's prime minister, said the four adults and five children killed in the blaze, and 20 of the 60 people injured, were Turkish.
"We are greatly concerned over the possibility of premeditation in the fire in which all the victims were Turks," he said, adding that a government official and four Turkish police officers would visit the scene of the fire.
A spokeswoman for Wolfgang Schaeuble, Germany's interior minister, confirmed Germany had accepted Turkey's request to send its own fire experts to take part in the investigation.
"The offer has been gladly accepted by the local authorities in Ludwigshafen," she told reporters.
She said the Turkish experts would work with a team of 50 German investigators.
Angela Merkel, the German chancellor, said it was "particularly upsetting that there are so many children among the victims".
Fire breaks out
The fire broke out during carnival celebrations in the city and the four-story house's wooden staircase swiftly collapsed, trapping people inside.
Many jumped, in some cases missing rescue nets laid out by police.
"The scenes were so terrible that some of the forces deployed wanted to give up their jobs afterward," Wolfgang Fromm, a German police chief, said.
A six-month-old baby girl, identified only as Onur, was thrown from a window and caught by police below.
She has been reunited with her father, who also escaped the blaze unhurt.
Onur's mother was still in hospital recovering from injuries, police said.
Police spokesman Michael Lindner said he could not rule out further victims, "but we hope we will not find any more people dead".
Rescue officers and investigators were still unable to enter the building on Tuesday because of the danger it might collapse.