More than 70 environment ministers meet in India on Wednesday for key talks on halting the depletion of Earth's natural resources, under pressure to put up money to match their political pledges.

The high-level gathering comes two years after UN countries agreed at a conference in Japan to reverse by 2020 the worrying decline in plant and animal species that humans depend on for food, shelter and livelihoods.

The 2010 meeting came up with a 20-point plan which is being hamstrung by a lack of money for conservation programmes at a time of global financial austerity.

"The critical issue really is how to mobilise the necessary financial, technical and human resources," Indian Prime Minister Manmohan Singh told delegates at a meeting in Hyderabad of the UN's Convention on Biological Diversity (CBD) on Tuesday.

The convention, to which 193 countries are signatories, marks its 20th anniversary this year.

In that time, it has already missed one key deadline when it failed to meet the target set to halt biodiversity loss by 2010.

Nearly half of amphibian species, a third of corals, a quarter of mammals, a fifth of all plants and 13 percent of the world's birds are at risk of extinction, according to the "Red List" compiled by the International Union for Conservation of Nature (IUCN) which is due to be updated on Wednesday.

A three-day minister's meeting from Wednesday to Friday comes at the tail-end of two weeks of negotiations by senior bureaucrats from 184 CBD parties -- talks that delegates say have become stuck on the question of financing.

"Obviously to some extent a financial crisis in many of the traditional donor countries is playing into the negotiations," UN Environment Programme executive director Achim Steiner told AFP.

"Also there is still work that needs to be done on what exactly is the financial framework, the order of magnitude that we are talking about."

The next 48 hours of negotiations, he added, "will be on amounts of money".

Sandrine Belier, one of three European Parliament negotiators in Hyderabad, added: "The European Union has not succeeded in forming a common position (on financing), and so it is silent."

Estimates vary, but experts say hundreds of billions of dollars will be required to achieve the targets set in Japan.

These include halving the rate of habitat loss, expanding water and land areas under conservation, preventing the extinction of species on the threatened list, and restoring at least 15 percent of degraded ecosystems by 2020.

Current conservation spending is estimated at about $10 billion per year.

"I urge the parties to the CBD to agree to some measures, commitments and targets of resource mobilisation, even if on an interim basis, so as to infuse confidence in parties and also to generate momentum," India's environment minister Jayanthi Natarajan told delegates on Tuesday.