Singapore is hosting US P-8 Poseidon spy planes for the first time, with the deployment set to last one week.
The announcement came on Monday as visiting Defence Minister Ng Eng Hen and his US counterpart Ashton Carter signed an enhanced Defence Cooperation Agreement at the Pentagon to broaden military ties between the two sides.
The pact, signed in conjunction with the 25th anniversary of a 1990 Memorandum of Understanding and the 10th anniversary of the 2005 Strategic Framework Agreement between the US and Singapore, outlines a wide range of areas where the two sides will deepen their cooperation, and also lists some new ones.
The Singapore Defence Ministry said the agreement lays out new areas of cooperation in humanitarian assistance and disaster relief, cyber defence, biosecurity and public communications.
It also introduces new high-level dialogues between the two countries' defence establishments.
During their meeting, Dr Ng and Mr Carter reaffirmed the importance of a strong US presence in the Asia-Pacific region.
A joint statement from the two defence chiefs "welcomed the inaugural deployment of the P-8 Poseidon aircraft", adding that it would "promote greater interoperability with regional militaries through participation in bilateral and multilateral exercises, while providing timely support for regional humanitarian assistance and disaster relief and maritime security efforts".
In the US, the deployment of the planes was the announcement that drew the most attention, with Washington pundits viewing the move as one that would bolster President Barack Obama's much-vaunted pivot to Asia.
"Singapore has given the United States strategic anchorage for more than two decades after the closing of US bases in the Philippines.
"This decision is significant because the US is seeking to build a regime of shared maritime domain awareness," said Dr Patrick Cronin, senior director of the Asia-Pacific Security Programme at the Centre for a New American Security in Washington.
"Singapore's security cooperation is helping to create enduring stability and transparency."
China, meanwhile, said the US deployment was aimed at militarising the region.
However, a spokesman for the US 7th Fleet has been quoted as saying that the move had nothing to do with US-China tensions in the South China Sea.
"It's not about the South China Sea, it's about partnership with Singapore and other partners in the region," Lieutenant Commander Arlo Abrahamson told the BBC.
The US has previously launched its P-8 planes - modified Boeing 737s which gather intelligence and can hunt down submarines - from bases in Japan and the Philippines, and has also conducted surveillance flights from Malaysia.
In Singapore, the planes started operating from Paya Lebar Airbase on Monday and the deployment will end next Monday.
Asked about future deployments, the US Navy did not want to go into details of specific dates, saying they were subject to ongoing planning and coordination.
Dr Ng will be in Washington until tomorrow. He will be meeting congressional leaders and high-ranking Pentagon officials, and is due to deliver a speech at the Centre for a New American Security, a think-tank.