Barack Obama is expected to offer guarded support for Japan in its bitter territorial dispute with China over a group of islands in the East China Sea, as Washington seeks to reassure its Asia-Pacific allies of its commitment to regional security in the face of an increasingly assertive China.

Obama will arrive in Tokyo on Wednesday at the start of an eight-day tour of Asia that will include South Korea, Malaysia and the Philippines.

On Tuesday about 150 Japanese politicians risked further souring ties with China by visiting Yasukuni, a shrine in Tokyo that honours Japan's 2.5 million war dead, including 14 leaders hanged for war crimes by the allies.

Three years after the US announced it would shift its attention from Europe and the Middle East towards the Asia-Pacific, Japan is seeking US support at a time of record Chinese military spending and concern over North Korea's nuclear weapons programme.

Discussions between Obama and the Japanese prime minister, Shinzo Abe, are expected to focus on Tokyo's longstanding dispute with Beijing over the Senkakus – known in China as Diaoyu – a group of uninhabited islands claimed by both countries.

The US is bound by a bilateral security treaty to defend Japan, although so far it has refused to take sides in the dispute in an attempt to avoid creating additional friction with China.

"The American objective is to reassure countries that … America is here to stay and is going to keep a strong interest in dealing with China together with those countries," said Koichi Nakano, a professor of political science at Sophia University in Tokyo.

A recent report by the Senate foreign relations committee urged Obama to "upgrade" US alliances in the Asia-Pacific and demonstrate "an enduring US commitment to the region, assuring our partners that we are in it for the long haul".

Abe, who took office in December 2012 with a nationalist agenda, will also seek US approval for his plans to bolster Japan's military, which for decades has operated in the shadow of the 50,000 American troops based in the country.

"I would like to send a message to the world that the Japan-US alliance will play a leading role in ensuring peace and stability in the Asia-Pacific region," Abe told visiting US officials this week.

On Monday White House officials reiterated that the US "will always honour its obligations to the defence of Japan". However, a joint statement that the leaders are due to issue on Thursday is likely to omit any mention of the Senkaku islands by name, according to Japanese media.

In a sign of how anxious Japan has become over potential threats to its thousands of outlying islands, it began its first military expansion in more than 40 years at the weekend, starting construction of a new base on the southern island of Yonaguni, which is located near the Senkakus.

Japanese and Chinese navy and coastguard ships have been involved in regular standoffs around the uninhabited islands since Japan bought them from their private owners in 2012. The purchase sparked riots in several Chinese cities.

Last November China raised the stakes when it unilaterally declared an air defence identification zone that overlaps Japanese airspace over the Senkakus. Japanese military aircraft scrambled jets a record 415 times in the year to March in response to flyovers by Chinese planes.

Obama's four-nation tour is supposed to demonstrate his commitment to following through on plans announced three years ago to pivot US influence towards the Asia-Pacific, a region with huge economic potential but beset by historical disputes and potential threats to stability.

The Obama administration at times has appeared disengaged from the Asia-Pacific, according to some critics, who point to last year's crisis on the Korean peninsula, when the US was wrong-footed by weeks of sabre rattling by the North Korean leader, Kim Jong-un.

Abe's election just over a year ago, which coincided with leadership changes in China and South Korea, has clearly caused anxiety in Washington as Japan's relations with its neighbours have sunk to their lowest level in decades.

Abe and his Chinese counterpart, Xi Jinping, have yet to hold formal talks. The depth of their animosity was in evidence on Tuesday when Beijing denounced the Japanese MPs' Yasukuni visit as a "slap in the face" to Obama.

A rare public show of US displeasure over Abe's pilgrimage to Yasukuni last December may have been a factor in his decision to forgo a second visit as leader.

Japanese media said the joint statement to be released by the leaders would stress the importance of the Japan-US alliance and commit both countries to resist any attempt to change the regional status quo by force, a reference to repeated incursions by Chinese ships into waters near the Senkaku islands, the Yomiuri Shimbun said.

White House officials have stressed that Washington's security commitments extend beyond Japan to include countries embroiled in separate disputes with China over territories in the South China Sea.

In a move likely to cause alarm in Beijing, Obama is expected to reach an agreement with the Philippines on better access to the country's airbases and ports for the US air force and navy, more than 20 years after the US closed its huge naval base in Subic Bay.

Obama's visit to South Korea will centre on security ties, but he is also expected to pay his respects to the 300 people believed to have died in the Sewol ferry disaster. "As I will underscore on my visit to Seoul next week, America's commitment to our ally South Korea is unwavering – in good times and in bad," he said last week.

US pressure succeeded in bringing Abe and his South Korean counterpart, Park Geun-hye, together for a meeting with Obama during the recent nuclear safety summit in The Hague.

But South Korea, where the US has 28,500 troops, and Japan remain at odds over ownership of the Takeshima islands – known by Koreans as Dokdo – and Japan's apparent lack of remorse over its use of tens of thousands of mainly Korean sex slaves before and during the second world war.

In Malaysia, where Obama will be the first sitting US president to visit since Lyndon Johnson in 1966, Obama will attempt to strengthen ties with the leadership despite concerns over its treatment of opposition politicians. US officials said there were no plans for Obama to meet the country's opposition leader, Anwar Ibrahim.

Security was tight in Tokyo before Obama's arrival, with 16,000 police officers deployed in anticipation of the first state visit by a US president since Bill Clinton in 1996.