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ndonesia has questioned the motive behind the United States’ move to turn Darwin, the Australian city closest to Indonesia, into a de facto US military base, warning that it could create mistrust among countries in the region.

“What I would hate to see is for the agreement to provoke a reaction and counter-reaction that would create a vicious cycle of tensions and mistrust,” Indonesian Foreign Minister Marty Natalegawa told a press briefing here on Wednesday.

US President Barack Obama and Australian Prime Minister Julia Gillard on Wednesday unveiled plans to deepen the US military’s presence in Asia-Pacific, by establishing a US base equipped with 2,500 US marines in Australia’s Northern Territory.

“With my visit to the region, I am making it clear that the United States is stepping up its commitment to the entire Asia-Pacific region,” Obama said in a joint conference with Gillard in Canberra, Reuters reported.

From next year, US troops and aircraft will operate out of Darwin, which is only 820 kilometers from Indonesia, from where they will be able to respond quickly to any humanitarian and security issues in Southeast Asia, where disputes over sovereignty of islands in the South China Sea are causing rising tensions.

“We have been informed by Australia on the matter. We’re not unaware. But it’s very important when a decision of this type is taken that there is transparency for the scenarios being envisaged, and that there is no misunderstanding and tension as a result,” Marty said.

Observers said the US was making a statement aimed at China — that it had a strong military presence in the area.

Hariyadi Wirawan of the University of Indonesia said that the US’ move was untimely and counterproductive when ASEAN, including Indonesia, had been working hard for years to create a more peaceful region.

“We will expect a reaction from China, while ASEAN countries that have problems with China, such as Vietnam and the Philippines, will welcome the move, possibly tearing ASEAN apart,” he said.

Lawmaker T.B. Hasanuddin said the US base in Darwin would create new tensions, and called on Obama to explain his motive to ASEAN.

Four ASEAN countries — Malaysia, the Philippines, Brunei and Vietnam — have territorial disputes in some areas in the South China Sea.

In a highly symbolic ceremony held aboard a guided-missile destroyer, US Secretary of State Hillary Rodham Clinton underlined America’s military and diplomatic support for the Philippines as the island nation engages in an increasingly tense dispute with China over claims in the resource-rich South China Sea.

Marty suggested that claimants to the maritime region should pursue the code of conduct negotiations, while apparently chiding China and the US.

“ASEAN will not let the region become a competition arena for countries who consider themselves as big powers, whoever or whenever they may be,” he said.

“We have an interest to make a clear code of conduct [for the South China Sea] so that concerns from non-Southeast Asian countries can be reflected based on the interest of ASEAN countries’ national interest.”