By Robert Evans

GENEVA, May 4 (Reuter) - International mediators said on Thursday Croatia and leaders of the rebel Croatian Serbs had agreed to hold talks on a global peace settlement in Geneva -- but not this week.

A statement from the mediators, Lord David Owen of the European Union and Thorvald Stoltenberg of the United Nations, said discussions were continuing to find "a mutually convenient date."

It was not immediately clear whether one of the two sides or both had resisted an invitation from Owen and Stoltenberg to hold urgent discussions in the Swiss city starting on Friday morning. The invitation was issued on Thursday.

But diplomats close to the International Conference on Former Yugoslavia (ICFY) which the two chair said the meeting had proven difficult to arrange at short notice. "Both sides felt it was a little too early," one said.

Other sources said it seemed likely the meeting would be held early next week. Lord Owen himself flew to Bonn to see German foreign minister Klaus Kinkel immediately after the announcement was issued by in Geneva.

He would return to London from Bonn, ICFY sources said. Stoltenberg was flying to Geneva on Thursday evening from Copenhagen, they added.

Owen and Stoltenberg, in the first major initiative by their Conference in the past year, had invited Hrvoje Sarinic, a top aide to Croatia's President Franjo Tudjman, and Milan Martic of the Croatian Serbs to the meeting.

He had suggested Martic, self-styled president of the Serbs' "Republic of Serb Krajina" to bring along his "prime minister" Borislav Mikelic and "foreign minister" Milan Babic.

The Croatian capital of Zagreb has been hit by rocket attacks by the Serbs twice in the past two days after the Croatian army seized control of a Serb-held region in southern Croatia.

Reports from the city say Croatians are widely blaming Martic for authorising the attacks, which have caused six deaths and many injuries from cluster bombs.

Owen told a news conference on Wednesday he and Stoltenberg feared tensions between the Croatians and the Croatian Serbs, who still control around one third of the country, could spark a wider war, perhaps between Croatia and Serbia.

"That is the big one....the extremely dangerous one," he said. Croatia and the rump Yugoslavia of Serbia and Montenegro fought a bitter war in 1991 on the breakup of the old Yugoslav federation.

It ended with a U.N.-brokered ceasefire in January 1992, with three major areas of Croatia controlled by Serbs who inherited heavy weaponry and equipment from the old Yugoslav army.

The Croatian army itself took control of one of these areas, Western Slavonia, in a lightning action on Monday and Tuesday. A ceasefire in the area was negotiated on Wednesday.