* Would be biggest-ever biodiversity-linked debt issuance

* March meeting sets roadmap, hurdles remain on structuring

* Colombia, Brazil sources caution on chance of 2024 deal

LONDON/SAO PAULO, April 18 (Reuters) - A political push to raise the first-ever "Amazonia Bond" has ramped up during talks to agree a "roadmap", yet the chance of a deal this year faces technical hurdles and scepticism among some of those tasked with managing the debt, sources told Reuters.

Brazil, Colombia, and Ecuador are among a group of nations in talks with development banks to launch a specially supported framework to raise billions of dollars of low-cost funding to protect the world's biggest rainforest.

Proposed by the Inter-American Development Bank and World Bank last year, Reuters is for the first time reporting the progress being made, the bond structures and timings being discussed, but also some of the push-back from officials in two of the region's biggest countries.

Covering more than 6 million square kilometers, the Amazon absorbs vast amounts of climate-warming greenhouse gases and is home to more than 10% of all known animals and plants, the highest density of species anywhere on Earth.

"It would be a major landmark transaction for nature-linked securities," said Arend Kulenkampff, director of the Sustainability-linked Sovereign Debt Hub, a non-profit effort to coordinate green financing, referring to the effort's potential impact.

COST OF STEWARDSHIP Politically, Amazonia bonds align with the call from the presidents of Brazil, Colombia and others in the Amazon basin for rich countries to contribute more to rainforest's protection.

A member of Brazil's climate delegation told Reuters that increasing multilateral development bank (MDB) financing is a top demand of it G20 presidency this year and ahead of the U.N. climate summits in Azerbaijan in November and its Amazonian city of Belem in 2025.

Only MDBs can rally climate financing on the scale that is needed in large developing countries like Brazil, Mexico and India, the person said. 'Credit guarantees' for example can sharply reduce borrowing costs that can normally be in the double-digits for countries.

How much money MDBs can provide and how fast is an open question, as officials say there is no time to waste in addressing climate change.

But while politically Brazil, and Colombia which hosts the COP16 U.N. biodiversity talks in October, are both keen to have a landmark deal to show for their efforts, some officials are sceptical of the need to rush a new debt instrument.

"Colombia, like the other eight Amazon countries, could launch an 'Amazon bond,' but it has insisted on thinking of the Amazon not as a source of debt but as a source of income," said Jose Roberto Acosta, Colombia's director of public credit at the finance ministry.

Emerging economies are increasingly pushing for the world to help put a value on their stewardship of such shared resources, for example by generating biodiversity credits that could be sold to other countries or companies to raise money.

"For this reason, it is not very likely that it will be achieved before COP16," Acosta said.

Two sources with direct knowledge of the matter told Reuters that discussions were still in preliminary stages within Brazil's government and that any progress, if confirmed, would not come this year.

Brazil's Finance Ministry, said it was "so far" unaware of any discussions and had not yet received a formal proposal for an Amazonia bond.

The ministry also pointed to last year's strong demand for Brazil's first international green bond that raised $2 billion and was sold with lower-than-normal 6% interest rate. It plans to issue more in the future it added, although banking sources suggested an MDB-guaranteed Amazonia bond might only need half that interest rate.

And there is need to keep borrowing rates as low as possible. The cost of hitting Brazil's self-set climate targets - it is aiming to more than halve its greenhouse gas emissions by 2030 and be 'net zero' by 2050 - has been estimated at $100 billion a year, or 7% of its economic output.

Other countries and the development banks involved in the plans did not comment on the status of talks when asked by Reuters.

MARCH TALKS

The March talks discussed a range of issues that will need to be agreed before the first bond is launched.

Among them was what to include on the "menu" of bond options open to countries issuing under the framework, with an aim of launching both "use of proceeds" bonds - where money is earmarked for specific projects - and "sustainability-linked bonds" (SLBs), tied to more general goals like reducing deforestation rates.

With most countries in the region yet to write SLB frameworks into national regulations, a use of proceeds bond is a more likely option for the first issuance, three sources said. Companies and local development banks may also issue in future.

International interest is strong, with individual governments including Sweden, Italy and Spain already providing support, three sources said. Going forward, other multilaterals such as the Development Bank of Latin America and the Caribbean (CAF) are likely to become involved, one source added.

Among other issues to resolve is defining what should be considered a legitimate use of the new bonds' proceeds, including whether to allow spending in cities, given 80% of those living in the Amazon are in urbanised environments.

While the first bonds are likely to be issued by countries individually, the hope is they could eventually be done jointly under the IDB's 'Amazonia Forever' framework to make large scale and effective cross-border conservation efforts possible.

The aim of the programme is to fund sustainable development and help reduce deforestation, with the equivalent of about four soccer pitches being cut down every minute, according to EU statistics.

While Brazil, Colombia, Ecuador, Guyana, Peru, Bolivia and Suriname have already signed up, issuing bonds jointly is no easy feat given the differing financial health of each state.

It follows a drive by Brazil's left-wing President Luiz Inacio Lula da Silva to unite his neighbours in pushing richer nations to help pay to protect the forest. Since 1970, Latin America has lost 94% of its monitored populations of mammals, birds, fish, reptiles and amphibians, a WWF and ZSL analysis showed.

(Additional reporting by Nelson Bocanegra in Bogota; Editing by Anna Driver)