The United Nations starts a last-chance bid Monday to agree on a treaty to regulate the $80 billion a year conventional arms trade, but the United States and other major powers have thrown up immediate obstacles.

The 193 UN members will have 11 days to hammer out a treaty that could force countries to evaluate, before making a sale, whether weapons will be used for human rights violations, or terrorism or organized crime.

UN leader Ban Ki-Moon along with a host of Nobel Peace Prize winners and pressure groups have urged the key powers to buckle down and make concessions. The omens are not good, however.

Four weeks of talks in July ended in failure. Major producers -- such as the United States, Russia and China -- and buyers -- including Egypt, India, Pakistan and the Gulf states -- battled to chip away at the sales conditions and even to exclude whole categories from the treaty.

The United States refuses to include ammunition. China wants to protect its small arms, while Russia opposed including gifts and transfers of arms that could be made to an ally.

A compromise document was drawn up, but the United States asked for more time. "Quite frankly, a lot of the other big producers were relieved," said one western diplomat.

The UN General Assembly has decreed that these will be the "final" negotiations.

"We really want to nail this thing now," said one European diplomat. "There is a willingness, but a lot depends on the US again."

The US State Department reaffirmed 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."

Eighteen Nobel Peace Prize winners, including former US president Jimmy Carter and South African campaigner Desmond Tutu, sent a letter to US leader Barack Obama saying he had a "moral duty" to seek a strong treaty.

Ban 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.

Lobby groups have condemned the existing draft that does not include ammunition, nor spare parts and components, arms intended for police use, drones and military helicopters.

Twelve billion bullets worth $4.3 billion are made each year, according to Oxfam. The United States produces half of them and the compromise accord drawn up last year only mentioned ammunition in an annex to the proposed treaty.

The text would also not cover military cooperation accords such as those under which Russia sends arms to Syria and France and Britain help their former colonies.

Amnesty International is demanding that the treaty cover as wide a scope as possible.

"History has shown that strong treaties create high international standards and bring about change, even for non-signatories," commented Oxfam's arms control specialist Anna MacDonald.

Diplomats said that a compromise text could be found, but this risked being weaker.

There could also be a campaign to rally a large number of countries around one strong draft and hope that refuseniks feel obliged to join. This was the tactic used for the Oslo Convention on cluster munitions in 2008. Seventy-nine countries have since signed up.

The key will be getting the major arms producers to join.

Amnesty 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.