WASHINGTON (AFP) - Washington signalled on Friday a looming showdown at the United Nations (UN) next week when members will try again to hammer out the first international treaty on the US$70 billion (S$87 billion) global arms trade.

The first bid to draw up an arms trade treaty came close to agreement but deadlocked in July, when, despite years of preparatory work, the United States (US) asked for more time to pour over the draft text.

US Secretary of State John Kerry said that the administration of President Barack Obama supported a treaty, due to be debated at a 10-day conference at the UN starting on Monday.

But he warned that the US "would only be party to one that addresses international transfers of conventional arms solely and does not impose any new requirements on the US domestic trade in firearms or on US exporters".

The Obama administration also opposes any text that goes against existing US law, including the Constitution and Americans' rights to bear arms under the Second Amendment.

One of the major sticking points is a call from many governments and activists to impose regulations on sales of ammunition - a move long opposed by the US, the world's leading arms producer.

"Ammunition is fundamentally different from weapons, and its inclusion would present a variety of practical and implementation difficulties," a US official told Agence France-Presse.

In his statement, Mr Kerry stressed that "the US is steadfast in its commitment to achieve a strong and effective Arms Trade Treaty that helps address the adverse effects of the international arms trade on global peace and stability." But he insisted the treaty must recognise "that each nation must tailor and enforce its own national export and import control mechanisms".

"We support a treaty that will bring all countries closer to existing international best practices, which we already observe, while preserving national decisions to transfer conventional arms responsibly," he added.

Amnesty International's North America deputy executive director, Mr Frank Jannuzi, argued that if US support is only "lukewarm", then other states "will take great comfort and will exploit that lack of leadership to opt out."

"At a minimum we need to capture within this treaty's provisions the export of munitions that allow these weapons to kill," he said.

"Amnesty's principle concern is that an AK-47 can last for three decades and without ammunition, it's a club."