BEIJING - China’s military will take “decisive” measures if there is a repeat attack by Myanmar forces on its territory, a senior military officer said after a bomb from a Myanmar aircraft killed four people.

Myanmar government forces have been battling rebels on the border with China since last month and China has urged Myanmar to “lower the temperature”.

But Myanmar denied that any bomb from its forces had fallen in China and said the rebels might have fired into China to create “misunderstanding”. The rebels do not have aircraft. China’s air force has dispatched planes to patrol the border and step up protection of its airspace. Beijing has also summoned Myanmar’s ambassador to complain about the bombing. Fan Changlong, who is a deputy head of the powerful Central Military Commission, said Myanmar air force aircraft had crossed the border “many times” recently, China’s defence ministry said in a statement late on Saturday.

“The Myanmar side must recognise the seriousness of the issue, seriously deal with this incident, punish those who caused the trouble, apologise and pay compensation to family members, and explain themselves to China,” Fan was cited as telling Myanmar’s military in an emergency telephone call.

Myanmar must take strict steps to rein in its armed forces to ensure no repeat of such incidents, he said.

“Otherwise, China’s military will take resolute and decisive measures to protect the lives, property and security of China’s people,” Fan said, without elaborating.

Speaking at his annual news conference on Sunday, Chinese Premier Li Keqiang said that the government had the ability and responsibility to “firmly defend” the stability of the border. Tens of thousands of people, many of them ethnic Chinese, have fled the fighting in northeastern Myanmar’s Kokang region into China.

Myanmar has said Chinese mercenaries were fighting with the rebels, and it has urged China to cooperate to prevent “terrorist attacks” being launched from Chinese territory.

China has denied that any attacks into Myanmar have been launched from its territory.

The rebels are from a group called the Myanmar National Democratic Alliance Army (MNDAA), which is led by ethnic Chinese commander Peng Jiasheng.

The MNDAA was formed from remnants of the Communist Party of Burma, a powerful China-backed guerrilla force that battled the Myanmar government until it splintered in 1989. The group struck a truce with the government which lasted until 2009, when government troops took over their region in a conflict that pushed tens of thousands of refugees into China’s Yunnan province.

China and Myanmar share a 2,000 km (1,250 mile) border, much of it remote and hard to access.

Meanwhile, Chinese Premier Li Keqiang on Sunday offered Japan a chance of improved relations - but only if Tokyo’s leadership honestly confronts the country’s World War II aggression against China.

This year marks the 70th anniversary of the end of the war, and amid strained ties Beijing frequently calls on Tokyo to take a “correct” view of the conflict and avoid glossing over responsibilities for atrocities during its invasion and occupation of large swathes of the country in the 1930s and 1940s. “It is true that the current China-Japan relationship is in difficulty,” Li told reporters, calling perceptions of the war the “crux” of the problem.

“At such a critical moment this year there is both a test and an opportunity for the China-Japan relationship,” he added, speaking at his annual press conference after the close of the country’s Communist-controlled National People’s Congress legislature.

“If leaders of Japan face history squarely and maintain consistency in how they view that part of history there will be a new opportunity for improvement and further growth of China-Japan relations,” he added.

He also said that such a stance would “create favourable conditions” to expand business relations between the world’s second- and third-largest economies.

Li’s comments and wording were in line with Beijing’s standard position, but were not as bombastic as the salvos of criticism frequently lobbed by Chinese foreign ministry officials at regular briefings and commentaries in state media.

He also took care to mention that the Japanese had also experienced pain during the conflict.

“The war of aggression imposed on the Chinese people by the Japanese militarists brought untold sufferings and the average people in Japan were also victims of that war,” he said.

China has in the past emphasised it has no quarrel with the Japanese people.

But Beijing - which regularly exploits nationalism as part of the Communist Party’s claim to a right to rule - is planning a major military parade to commemorate the end of the war.

Li did not address the impact the event might have on Japanese sentiments, but said it was intended to “bear in mind the hard lessons gained from the past and ensure that that kind of history will never repeat itself”.

“The purpose is to uphold the outcomes of the Second World War and the post-war international order and international laws to maintain enduring peace of mankind,” he added.

Japanese Prime Minister Shinzo Abe is a staunch nationalist who has questioned how far Tokyo should continue atoning for the conflict while calling it to beef up its military might.

In comments seemingly aimed at his Japanese counterpart, Li said: “For leaders of a country, while inheriting the historical achievements made by their predecessors, also need to show the historical responsibilities for crimes committed in the past.”

Chinese foreign minister Wang Yi said at a press conference a week ago that Abe will only be welcome at Beijing’s commemorations if he is “sincere” about history.