The signing of the declaration on the renewal of the Strategic Arms Reduction Treaty (START) has been expected to be a major outcome of the summit meeting between Obama and his Russian counterpart Dmitry Medvedev.

"I can confirm that the final agreement of the document has not been completed," a source in the Russian foreign ministry described as a high ranking diplomat told the Interfax news agency.

Issues still to be resolved include problems related to the parameters for reducing the number of carriers of nuclear warheads on both sides, the source was quoted as saying.

Russian officials have said the declaration on replacing the START -- which expires in December -- will broad political document with a set of guidelines for agreeing a formal deal later this year or early 2010.