The four Indo-Pacific leaders of the "Quad" grouping vowed on Tuesday to stand together for a free and open region at the start of talks, vowing also to work on fighting climate change.

U.S. President Joe Biden and his counterparts from Australia, India and Japan began discussions aimed at countering an increasingly assertive China and paving over differences on issues including Russia.

Biden, Indian Prime Minister Narendra Modi, Japanese Prime Minister Fumio Kishida and new Australian Prime Minister Anthony Albanese will also hold bilateral meetings, with Modi set to meet Kishida for talks and a working dinner after the larger talks have finished.

Taiwan was not an official item on the Quad agenda, a U.S. official said, but it was expected to be a key topic when the four leaders meet a day after Biden broke with convention and volunteered U.S. military support for the self-governed island claimed by China.

India frustrated the United States with what Washington regarded as a lack of support for U.S.-led sanctions and condemnation of Russia's invasion of Ukraine.

But Western officials decided to push Modi on the issue gently and privately, seeking instead to emphasize their shared views on China, which Washington views as a bigger long-term challenge than Russia.

India has developed close ties with Washington in recent years and is a vital part of the Quad grouping aimed at pushing back against China.

But it has a long-standing relationship with Moscow, which remains a major supplier of its defense equipment and oil supplies. India abstained in U.N. Security Council votes on the issue, though it did raise concerns about some killings of civilians in Ukraine.

"The president is very aware that countries have their own histories, they have their own interests, they have their own outlooks, and the idea is to build on commonalities," said another U.S. official who briefed reporters and declined to be named.

One key question for Washington going into the Quad meeting was how to wean India off Russian-supplied military equipment and whether to provide defense aid and other support to India to accelerate that transition.

The United States is considering "investment support" of $4 billion for India on top of billions of dollars extended earlier, New Delhi said on Monday after the two sides signed an agreement for COVID-19 vaccine manufacturing, healthcare, renewable energy, financial inclusion and infrastructure.

India also joined the United States and 11 other countries in Washington-led economic talks called the Indo-Pacific Economic Framework for Prosperity (IPEF).

The Quad largely agrees that the situation in Ukraine is a serious threat to the international order but it remained unclear how directly they would address that matter in a joint statement, the second U.S. official said.

He added that the Quad needs to reinforce itself before thinking about whether to adopt other potentially interested members, such as South Korea.