The Defense Ministry is urging its officials and senior Self-Defense Forces officers not to invite to their events any guest who may make political remarks, several ministry and SDF sources said Tuesday.

The move came after a guest speaker at the Nov. 3 air show at the Air Self-Defense Force's Iruma Air Base in Sayama, Saitama Prefecture, harshly denounced Prime Minister Naoto Kan, saying "let's topple the Democratic Party of Japan-led administration soon. All of you must feel the same in your heart," according to the sources.

Some DPJ lawmakers who attended the event expressed displeasure over the remarks and told the ministry to take preventive steps at future events.

The ministry issued a notice last Wednesday titled "Securing political neutrality" under the name of Vice Defense Minister Kimito Nakae, the sources said.

The notice urges officials to ask outside organizations to avoid taking any misleading actions that could suggest they are politically active when they participate in events at defense-related facilities.

It says the ministry and SDF officers should also ask outside groups to refrain from taking part in such events if there is a possibility that their actions could be misleading, the sources said.

The notice has sparked controversy, with some defense officials questioning whether it infringes on freedom of speech.

"I understand that it is a countermeasure taken only because the DPJ administration was criticized," a senior SDF officer said. "If it were against the (opposition) Liberal Democratic Party, there would have been no notices like this."