Four days of high-level talks on a free trade deal closed in Singapore with wide gaps remaining between the 12 participating countries.

Negotiators were unable to narrow differences that need to be resolved if the so-called Trans-Pacific Partnership (TPP) is to go ahead.

The US led talks today (Tuesday) on the environment and labor issues.

But with countries hardening their positions, some delegates left their seats.

The talks closed without any progress between the US and Japan on farm products and automobiles, which observers say are the key to a deal.

Japan wants to preserve high tariffs in five farm categories such as rice and beef. The U.S.-led TPP insists on eliminating those trade barriers entirely.

Japanese Economy Minister Akira Amari warned the talks could drift if allowed to go on at length.

Observers say that Japan was prepared to make concessions, but that the US farm lobby stuck to demands for a complete lifting of import duties.

Many other issues remain outstanding between the 12 countries in the TPP talks.

The next chance for dialog comes when President Obama visits Japan in April, but the outlook for progress remains murky.