Talks resumed on Monday on a United Nations treaty to regulate the sale of conventional arms - amid roadblocks put up by some of the world's key players.
After four weeks of negotiations failed in July, the 193 members of the global body will again attempt to hammer out an accord that could force states to assess, before making a sale, whether weapons will be used for human rights violations, terrorism or organized crime.
But hurdles loom large since major arms producers and buyers have fought to chip away at the sales conditions and even to exclude whole categories from the treaty.
The United States, for one, refuses to include ammunition. China wants to protect its small arms, and Russia opposed including gifts and transfers of arms that could be made to an ally.
The US State Department reaffirmed on Friday that it opposes any treaty that includes ammunition because of the financial and administrative burden of keeping checks.
"The United States is steadfast in its commitment to achieve a strong and effective Arms Trade Treaty," said Secretary of State John Kerry.
But he added that his country, the world's top arms producer, could only agree on a "treaty that addresses international transfers of conventional arms solely."
UN Secretary-General Ban Ki-moon meanwhile called for a treaty that includes ammunition.
"It is our collective responsibility to put an end to the inadequate regulation of the global trade in conventional weapons -- from small arms to tanks to combat aircraft," he said.
As talks were about to get underway, Amnesty International urged action by pointing to conflicts in Syria, Mali and elsewhere.
"Syria, Mali, the Democratic Republic of the Congo and Sri Lanka are just a few recent examples where the world bore witness to the horrific human cost of a reckless global arms trade steeped in secrecy," Salil Shetty, Amnesty International's secretary general, said in a statement.
"It shouldn't take millions more dying and lives destroyed before leaders show some backbone and take action to adopt global standards to effectively control international arms transfers."
Amnesty has highlighted how the five permanent members of the UN Security Council - Britain, China, France, Russia and the United States - account for more than half the global sales of conventional arms.