Japan's defence minister on Friday warned Tokyo could send troops to a chain of East China Sea islands at the centre of a territorial row with China if the simmering dispute escalated.
Satoshi Morimoto said Tokyo's position had not changed, but confirmed that it would use force to defend the islands known as Senkaku in Japanese and Diaoyu in Chinese.
"Senkaku or not, defence of islands is principally conducted by the coastguard and police," Morimoto told reporters in Tokyo.
"However, the law stipulates that Self-Defense Forces troops can act" if local authorities are unable to handle the situation.
His comments came a day after Prime Minister Yoshihiko Noda told parliament he would take "stern actions" against any "illegal actions" on Japanese territory.
"If illegal actions are made by neighbouring countries in our territorial soil and waters, including Senkaku, we will take stern actions including using of Self-Defense Force troops, if necessary," Noda said Thursday.
"(But) it is important that we adopt a solid crisis-management framework and make diplomatic efforts to prevent situations from developing to such an extent," he added.
Chief Cabinet Secretary Osamu Fujimura, the government's top spokesman, played down Noda's remarks on Friday, saying he had just responded to a hypothetical question about a Chinese military attack.
"Prime Minister Noda was referring to a theoretical possibility and referred to the use of Self-Defense Forces troops," Fujimura said, adding that the remark was not specifically directed at China.
Tensions between the two countries rose earlier this month after Chinese vessels twice entered waters near the resource-rich islands, which are claimed by Beijing and Tokyo.
Japan lodged two formal complaints with Beijing last week and summoned the Chinese ambassador to Japan in protest.
The uninhabited outcrops were the scene of a particularly nasty spat in late 2010 when Japan arrested a Chinese trawlerman who had rammed two of its coastguard vessels.
Tensions spiked in April after controversial Tokyo governor Shintaro Ishihara, an outspoken critic of Beijing, called for Tokyo to buy the islands from their Japanese owner.
Japan's premier has said the central government was also considering buying the island chain, sparking an angry response from Beijing.