The government has decided to postpone drills with foreign troops, based on security legislation that expanded the activities of the Self-Defense Forces, until after the Upper House election this summer, sources close to the matter said Sunday.

It is feared the joint drills would have an adverse impact on the ruling parties' performance in the election, the sources said. The legislation, which came into effect in March, enables Japan to exercise the right to collective self-defense — or coming to the aid of friendly nations under armed attack even if Japan itself is not attacked.

The sources added that the United States has expressed dissatisfaction after a bilateral command post exercise, called Keen Edge, conducted by the SDF and U.S. forces earlier this year, failed to take account of the expansion in SDF activities, even though the security legislation was enacted last September.

Although the U.S. forces requested that Japan expand the range of activities in Keen Edge, which was conducted between Jan. 12 and Feb. 2 at Yokota Air Base in western Tokyo, the SDF refused, saying it was "premature," the sources said.

The landmark defense policy shift has drawn strong opposition among the public who fear it could erode Japan's postwar pacifism.

In the latest Kyodo News poll conducted Friday and Saturday, 59.5 percent of respondents said they will decide on which candidate or political party to support in the House of Councilors' election based on their stance on the security legislation.

Tokyo has already told Washington that the SDF will not conduct drills reflecting its expanded role at the upcoming Rim of the Pacific Exercise, or RIMPAC, to be organized by the U.S. Navy this summer, the sources said.