FRANKFURT (Reuters) - Sony's joint venture with cell phone maker Ericsson must do better, Sony's chief executive was quoted as saying by a German newspaper on Wednesday.

Asked whether Sony is planning to end its Sony Ericsson joint venture, Howard Stringer told Die Welt: "It's certainly been a difficult year but buying out a partner is never an easy thing."

Sony lowered its group net profit forecast for the year to March by 17 percent, citing a slump at Sony Ericsson and weakening prospects for its electronics division amid tough price competition.

"We have to work together again as we did two years ago. Or the joint venture will have to find its own solution," Stringer said.

He added that it was hard for a company to be as nimble as possible when it works in a joint venture.

"You're always engaged in discussion and negotiation. We and Ericsson are always discussing ways of making Sony Ericsson as successful as it possibly can be," he said.