The U.S. military’s top officer in the Pacific urged Indian officials Wednesday to pursue even closer military ties with the United  States — part of a broader effort by the Pentagon to strengthen a relatively new partnership in the region, as China expands its military footprint in ways that alarm its neighbors.

Adm. Harry Harris, commander of U.S. Pacific Command, said that  expanded cooperation between the United States and India will not only be critical to Washington’s re-balance toward the Pacific, but “will arguably be the defining partnership for America in the 21st century.” He said he shared a vision with U.S. Ambassador to India Richard Verma that Indian and U.S. naval vessels will soon steam together “as we work together to maintain freedom of the seas for all nations.”

The comments came as India has moved to strengthen partnerships not only with the United States, but with Australia, Japan and other U.S. allies in the region. India also has voiced opposition to some of China’s actions in the East and South China seas, where Beijing has attempted to assert its sovereignty.

“This is ambition in action,” Harris said, speaking at the Raisina Dialogue, a conference in New Delhi focused on geopolitics and geo-economics. “It ensures the vision of our country’s leaders by strengthening military-to-military collaboration and in the process, it will improve the security and prosperity of the entire region.”

Harris’s comments also came as the Obama administration’s ability to curb China’s ambitions have been called into question by analysts. China has installed military radar, HQ-9 surface-to-air missiles and fighter jets on several atolls in the South China Sea in recent months. Defense Secretary Ashton B. Carter and other U.S. officials have said repeatedly that China’s rise is not a problem, but the way it is exercising its power can be.

Carter and Frank Kendall, undersecretary of defense for acquisition, technology and logistics, are expected to visit India next month as the two countries continue to deeper relations. It will mark Carter’s second trip to India in a year, and comes after the Navy’s top officer, Adm. John Richardson, visited last month along with the heads of other navies, including China’s, Russia’s and Iran’s.

Harris did not mention China directly in his latest remarks, but clearly seemed to call the country out.

“While some countries seek to bully smaller nations through intimidation and coercion, I note with admiration India’s example of peaceful resolution of disputes with your neighbors in the waters of the Indian Ocean,” Harris said. “India, indeed, stands like a beacon on a hill, building a future on the power of ideas… not on castles of sand that threaten the rules-based architecture that has served us all so very well.”

One of the great concerns about the South China Sea is whether China will seek to cut off or control international navigation on water and in airspace. The United States has carried out two so-called “freedom of navigation” exercises in the region in recent months, sending Navy destroyers near Chinese claimed islands and saying the missions demonstrate that free passage is still open to all nations.

Harris touched on the issue Wednesday, saying India, Japan, Australia, the United States and other like-minded nations can operate “anywhere on the high seas and airspace above them” outside of recognized territorial areas. China has rebuked the recent U.S. freedom of navigation exercises as provocative.

“The idea of safeguarding freedom of the seas and access to international waters and airspace is not something new for us to ponder – this is a principle based upon the international, rules-based global order that has served this region so well,” Harris said. “And for decades, the United States has conducted freedom of navigation patrols – or FONOPs – without incident. No nation should perceive FONOPs as a threat.”

Adm. Scott Swift, the senior officer for the Navy’s Pacific Fleet, said in a phone interview Friday that China’s direction has created a “general sense of angst” among other nations in the Pacific region. But he added that it isn’t just the South China Sea where concerns are being raised.

“That behavior and activity can be described as an arc,” Swift said. “We’re not sure where that arc is going to terminate… but there is a strategic plan that is being implemented.”

The United States has sought to counter that arc by deploying ships, aircraft in and troops in new locations and by strengthening ties with countries in the region. While many of the partnerships Washington has relied on there are decades old, the relationship with India — formerly a non-aligned power in the Cold War that had warm relations with the Soviet Union — has changed significantly in the last few years. Carter and Indian Defense Minister Manohar Parrikar reached an agreement late last that calls for a series of joint military exercises this year.

“This kind of progress is, frankly, stunning,” Harris said Wednesday. “We went from rarely talking only a few years ago to not only talking together, but doing together. Skepticism, suspicion, and doubt on both sides have been replaced by cooperation, dialogue, and trust.”

Swift said there is also a desire to increase the number of amphibious ships he has in the region by one or two, which would allow Marines and sailors to train more with other nations in the region. They’d likely transport Marines who are based in Darwin, Australia, where they have been based on a rotational basis since 2013. The deployment prompted China to accuse the United States of escalating military tensions.

India also is expected to participate in the Navy’s biannual Rim of the Pacific (RIMPAC) exercise in and around Hawaii beginning in June. China was invited for the first time in 2014, and is expected to participate again this year again with more than dozen other countries.

Swift said there are benefits to having China involved, and that he and Richardson, the Navy’s chief of naval operations, remain advocate of its participation.

“I think it’s so easy to judge because it’s so hard to understand what we get out of RIMPAC is a much deeper understanding not just of operating together, but an understanding of… that sense of angst that is here in the theater because of a lack of transparency,” Swift said. “I think we have a much higher probability of understanding what Chinese goals are by interacting with their sailors on a regular basis as we do throughout RIMPAC.”