Evan Medeiros, left, and fellow presidential advisers Tom Donilon and Danny Russel take notes as President Obama speaks with a foreign leader on the phone in the Oval Office on March 14, 2013. (Pete Souza - White House via CNP Photo )

President Obama's top adviser on Asia policy is leaving his post at a time of growing uncertainty over China's assertive behavior in the region, raising questions over the administration's strategy ahead of a high-stakes visit from President Xi Jinping in the fall.

Evan Medeiros, a China expert who has worked at the National Security Council during all of Obama's tenure, will step down as the agency's Asia director on Thursday, officials said. He will be replaced by Daniel Kritenbrink, the deputy chief of mission at the U.S. Embassy in Beijing.

White House officials said the personnel change did not portend any shift in U.S. policy toward China. Foreign policy experts in Washington who know Medeiros described his departure as a personal decision after a long run at the NSC, where officials work long hours under high-pressure situations.

"Among the allies, Evan got high marks for his strategic approach," said Michael Green, an analyst at the Center for Strategic and International Studies who served as Asia director under President George W. Bush. "There's a logic to him leaving on his own terms."

In a statement, NSC spokesman Alistair Baskey called Medeiros "a key architect of the president's Asia rebalance strategy, and especially toward China. He helped restructure the content and operation of our China policy in ways that shaped China's choices as a rising power."

Mederios has described the administration's strategy in dealing with Beijing as one of managing differences and accentuating areas of mutual interest. Last fall, Obama and Xi struck a major climate accord to reduce carbon admissions, which Obama has called an important step toward a larger, global climate deal that could be reached by the end of the year.

But since then, relations between China and the United States have grown increasingly strained. China has ramped up maritime operations in the South China Sea, a crucial shipping lane for many Asian nations, angering its neighbors and U.S. military leaders. Two weeks ago, the Chinese navy repeatedly warned a U.S. surveillance plane to leave airspace near a series of disputed islands.

Meanwhile, anti-China rhetoric has increased on Capitol Hill, as lawmakers weigh Obama's push for the 12-nation Trans-Pacific Partnership, a sweeping free trade and regulatory pact. Obama has described the TPP, which does not include China, as a way to ensure the United States crafts economic rules in fast-growing markets in Asia.

Foreign policy experts in Washington have begun calling on the Obama administration to adopt a tougher security stance on Beijing. Secretary of State John F. Kerry and Defense Secretary Ashton Carter have both warned Beijing in recent weeks to back off its military operations in the South China Sea.

The Obama administration had attempted to curry a better relationship with Xi after a rocky start with his predecessor, Hu Jintao, during Obama's first term. Xi will arrive in Washington for his first state visit in September, and some analysts said Medeiros's departure means there is unlikely to be a major diplomatic breakthrough.

Others described National Security Adviser Susan Rice as being too consumed by problems in other parts in the world--including a pending nuclear deal with Iran, Israeli-Palestinian relations, the U.S. effort to combat the Islamic State militant group, and the security situation in Ukraine--to focus on China.

Medeiros served as the NSC's China director before taking over as Asia director when Danny Russel moved from the White House to become the assistant secretary of state for East Asia and Pacific affairs in 2013.

Kritenbrink, who has been at the embassy since 2013, also has a deep background in China at the State Department and he has also served in Japan. He speaks Mandarin and Japanese. His first big test will be the visit to the White House of South Korean President Park Geun-hye in two weeks.