US Army chief Randy George said the region was "critically important", speaking to reporters alongside his Indian counterpart Manoj Pande, and vowed to boost cooperation to "maintain a free and open Indo-Pacific".

Generals from Japan and Australia, which make up the "Quad" defence cooperation forum alongside Washington and New Delhi, also took part, as did Britain and France.

As the generals met, China's Foreign Minister Wang Yi said that Beijing would oppose the "wanton expansion of military alliances", the latest in a string of warnings as Washington deepens security ties in the Asia-Pacific.

Beijing has long said that any effort to establish a NATO-like military alliance in the Asia-Pacific would provoke conflict.

Nations present at the two-day conference in New Delhi included Vietnam and the Philippines, both of which have longstanding pending territorial disputes with China.

The conference, which launched in 1999, brings together army chiefs and top officers from 30 countries.

India's Pande said the region faced challenges on both land and at sea.

"These range from territorial disputes over land masses, or in some cases, even over artificially expanded islands to acquire real estate and establish military bases," Pande added, in an indirect reference to China.

India has also had to balance its traditional alliance with Russia -- the provider of most of its arms imports, and now a source of cut-price oil -- with growing ties to Washington.

"The partnership between India and the US armies is vital for stability in the region, and the relationship between our armies is strong and growing stronger," George said.