Japan has opened up a new front in its territorial disputes with China and South Korea, after the education ministry instructed teachers to describe two contested groups of islands as integral parts of Japanese territory.

The ministry said on Tuesday it had revised teaching guidelines to make it clear that the Takeshima islands in the Japan Sea belong to Japan and are being illegally occupied by South Korea.

The Senkaku islands, which are controlled by Japan but claimed by China, will be described for the first time in classrooms as Japanese territory.

Current textbooks do not mention the Senkaku dispute and refer only to differences on Takeshima – another island group that is the subject of conflicting claims by Japan and South Korea.

The education minister, Hakubun Shimomura, said the teaching manuals had been changed to reflect the government's stance on Japan's history, including its territorial claims.

He said: "From an educational point of view, it is natural for a country to teach its children about integral parts of its own territory. We must make efforts to politely explain our position to both nations and seek their understanding."

The announcement quickly drew protests from Seoul and Beijing. South Korea's foreign ministry summoned Japan's ambassador to lodge a protest and demanded that the revisions be scrapped.

The ministry said in a statement: "Our government strongly condemns this and asks Japan to immediately withdraw it. If Japan truly hopes to contribute to world peace, it should nurture peace and reconciliation in the minds of its next generation, not plant the seeds of conflict and dispute."

Takeshima, known in South Koreans as Dokdo, is protected by a small police garrison and is home to just two permanent residents – an elderly fisherman and his wife. The rocky islets lie roughly equidistant between the Japanese and South Korean mainland in a stretch of water referred to as the East Sea by Koreans.

A spokeswoman at the Chinese foreign ministry, Hua Chunying, told reporters: "We once more urge Japan to respect historic realities, stop provocations and teach the younger generation a correct historical perspective."

It is the first time teachers have been encouraged to refer to the Senkakus as part of Japan, a shift that reflects Prime Minister Shinzo Abe's desire to ditch "masochistic" appraisals of the country's wartime history, promote its territorial claims and instill feelings of patriotism among schoolchildren.

Earlier this month, the education ministry said future textbooks would have to reflect the government's official position on contentious historical issues.

Critics believe that will mean omitting, or at least watering down, descriptions of wartime atrocities, including the Japanese imperial army's use of tens of thousands of sex slaves before and during the second world war, and the Nanking massacre, in which an estimated 300,000 Chinese citizens were killed by Japanese troops.

Despite frequent sightings of Chinese surveillance vessels in waters near the Senkakus, Japan insists there is no dispute over their ownership. Beijing stepped up its claims to the islands – known as the Diaoyu in China – at the end of last year when it declared an air-defence identification zone in the region that overlaps with Japan's.

Ties between Beijing and Tokyo deteriorated in autumn 2012 after Japan bought the islands from their private Japanese owners, sparking violent protests in several Chinese cities.

The teaching revisions will add to already strained tied between Japan and its neighbours over ownership of the island groups and disputes over its revisionist take on wartime history.

South Korea and Beijing have also voiced alarm at Japan's recent rise in military spending and plans by Abe to revise the pacifist constitution to allow its armed forces to play a greater role overseas.

The teaching guidelines, which are not mandatory, will apply to history, geography and civic classes at junior and senior high schools from April 2016. They were announced just days after the new chairman of public broadcaster NHK, Katsuto Momii, triggered anger in the region by defending Japan's wartime use of sex slaves. Momii has since expressed regret for the remarks, describing them as extremely inappropriate.