RIYADH, Saudi Arabia » U.S. Secretary of State John Kerry is pressing for peaceful resolutions to increasingly tense maritime disputes in Asia and urging China to take a firmer stand on North Korea’s nuclear program after its recent bomb test.

Set to leave Saudi Arabia on Sunday, Kerry planned stops in Laos, Cambodia and China, shifting his focus as he wraps up an around-the-world diplomatic mission that began in Switzerland with a heavy emphasis on the Middle East, particularly Iran and efforts to bring an end to Syria’s civil war.

His first stop is Laos, the current head of the Association of Southeast Asian Nations, whose members are becoming more vocal in complaints about China’s growing assertiveness over competing claims in the South China Sea and whose leaders President Barack Obama will host in California next month. Before that summit, U.S. officials say, Kerry will make the case to the leader of the 10-nation bloc to present a unified stance in dealing with China on the disputes, which have grown more intense as China continues to construct man-made islands and airstrips in contested areas.

The United States and governments with rival claims with China in the disputed region, including the Philippines and Vietnam, have expressed alarm over the Chinese construction, saying it raises tensions and threatens regional stability and could violate freedom of navigation and overflight.

But ASEAN unity has not always been possible as China wields great influence among some of its smaller neighbors, such as Cambodia. Cambodia held the ASEAN chair in 2012 and blocked the group from reaching consensus on the South China Sea issue and has frequently sided with China on the matter. A senior State Department official accompanying Kerry in Asia said the U.S. had heard from regional leaders that problems related to Cambodia’s chairmanship “left a black mark on ASEAN and are not to be repeated.” The official said the U.S. believed that Laos would do a better job in balancing ASEAN interests with China.

Recent developments, including China’s movement of an oil rig into a disputed zone and warnings against overflight of what it claims to be its territory, have raised levels of concern in the region to a point where the official said it would be very difficult for an external power like China to manipulate individual ASEAN countries in a way that paralyzes the broader group. The official spoke on condition of anonymity because he was not authorized to discuss the details of Kerry’s visit publicly.

Kerry will be only the second secretary of state to visit Laos since 1955 — Hillary Clinton visited in 2012. And Obama will become the first U.S. leader to visit the landlocked nation later this year. Laos has moved away from a communist system in the past two decades, but like its close ally Vietnam, it retains a one-party political system and its government has been criticized for being intolerant of dissent.

Laos was targeted heavily by U.S. bombing during the Vietnam War and still has large amounts of unexploded ordnance littering its countryside. The U.S. has stepped up efforts to help clear Laos of those bombs and Kerry is expected to commit to expanding and upgrading such programs with details to be announced when Obama visits later in 2016, the U.S. official said.

In Cambodia, Kerry is expected to note the country’s strong economic growth but also raise concerns with longtime authoritarian Prime Minister Hun Sen about human rights and political freedoms. Kerry plans to meet representatives of Cambodia’s opposition, led by a man who has been in self-imposed exile since November, when an order for his arrest was issued on an old conviction for defaming Cambodia’s foreign minister.

Kerry will wrap up his Asia tour in Beijing, where he will renew concerns about China’s aggressive behavior in the South China Sea and call for Chinese leaders to take more steps to press North Korea on its nuclear program. Since North Korea’s nuclear test earlier this month, U.S. officials asserted that China must use its leverage to demand that the Stalinist North Korean leadership end its nuclear weapons program and testing and return to six-nation talks aimed at denuclearizing the Korean peninsula.

The senior U.S. official said the U.S. believes that the pressure China has exerted on North Korea so far has not been enough to change the calculus of North Korea’s young leader, Kim Jun Un, and that it is important for China to join the U.S., South Korea and Japan in presenting a united front, which “must be a firm one, not a flaccid one.”

The official said the U.S. wants the Chinese to line up with Seoul, Washington and Tokyo in convincing North Korea that the peaceful way forward is to comply with U.N. Security Council resolutions but “continuing down the road of provocation is a dead-end street.”