Sri Lankan President Chandrika Kumaratunga says there is no agreement yet with the Tamil Tiger rebels about how to resume stalled peace talks.
Mrs Kumaratunga has not confirmed the August timeline
She said she wanted to discuss plans for self-government in rebel areas.
But, in a TV address, she stressed this could only be done as part of talks on a final peace deal.
Tamil politicians said on Thursday after meeting the president that she had expressed willingness to negotiate the single issue of self-government.
Mrs Kumaratunga has long resisted the Tigers' demand that their plan for self-government of the island's north and east should be discussed first.
'Committed to ceasefire'
In her national address on Saturday, she said there had been no breakthrough.
However she insisted that both sides were committed to the ceasefire.
"The delay in agreement on the agenda reflects the complexity of the peace negotiations," she said.
The Tigers walked out of peace talks in April last year
"It also indicates that we are taking negotiations very seriously and want to prepare in a thoughtful manner."
The speech appears to contradict a statement on Thursday by Joseph Pararajasingham, a member of the Tamil National Alliance - a group allied with the rebels.
After a meeting with Mrs Kumaratunga, he said: "The president told us she is willing to discuss the interim administration proposal without any precondition."
"We have reasons to believe that the talks will start in August."
A ceasefire has largely held between the Tamil Tigers and the government since February 2002.
However the Tigers walked out of peace talks in April last year.