Citizens demanding the return of a U.S. base in central Tokyo cited a written agreement Monday that they claim proves the heliport section of the compound is trespassing on Japanese soil. The Executive Committee for the Removal of the Azabu Heliport released a statement on an agreement regarding the 4,300-sq.-meter plot within the 3-hectare Akasaka Press Center, located in Minato Ward's Metropolitan Aoyama Park. The plot was temporarily provided to the military during the city's construction of the Roppongi Tunnel beneath the base in August 1983, but U.S. forces have continued using the plot since construction was completed in 1993. The agreement specifies that the arrangement was to be temporary and that the Tokyo Metropolitan Government must cover the cost of relocating the heliport. "Tokyo Gov. (Shintaro) Ishihara has had no qualms about saying 'no' to the U.S. before," said Hiroshi Itakura, a University of Tokyo employee and member of the citizen's group. "We want him to make a stand here, where it is clear that the U.S. forces are violating a contract agreement." But the situation is not as clear-cut as a contract infringement, experts say. The heliport is on national land, as is the rest of Aoyama Park, which Tokyo rents, so the metropolitan government cannot technically ask for the land back. The metro government has submitted multiple requests to the Defense Facilities Administration Agency since 1992 asking permission to fulfill their obligation to relocate the heliport.