CBI sources said influential connections of middlemen in the countries of their operation and layered international transactions are making it difficult for the agency to get information from abroad which is adversely affecting its probes.
The sources said the agency has registered 22 cases related to defence matters since 2004 in which nine are related to Tehlka expose, 11 related to defence related purchases and two pertain to secret documents held by private people.
In 14 cases, CBI has filed charge sheet while in six investigations are on.
The agency has closed two cases related to alleged irregularities in up-gunning of 130 mm field guns to 155 mm calibre by an Israeli firm Soltam and purchase of Terminally Guided Munition from a Russian firm Krasnapol, they said.
Both the cases were exposed through Tehelka sting operation and pertain to tenure of former Defence Minister George Fernandes.