Adrian Severin says the investigation's mandate should be "to investigate the responsibility of senior officials of the government of Belarus."
The victims, three Belarusians and a Russian journalist, disappeared in 1999 and 2000.
The report was due to be presented on September 19, but has now been rescheduled for September 27.
Severin hinted on September 20 that governments with close ties to Belarusian President Alyaksandr Lukashenka were behind the delay.
Severin told journalists that the problem was "not a lack of time but a lack of will" on the part of some members.
He said it was "quite obvious that Cuba was filibustering," but declined to name other countries.
The report will also express concern at "the steady deterioration" of the human rights situation in Belarus in 2005 and 2006.
Belarus has rejected the report as "artificial and politically motivated."