(Updates with further details about bank membership in third paragraph.)

CANCUN, Mexico -(Dow Jones)- The U.S. government on Saturday surprised members of the Inter-American Development Bank by laying down new conditions before putting extra money into the multilateral lender, according to a senior Brazil official.

"I only found out about this today," Planning Minister Paulo Bernardo told reporters on the sidelines of the IDB's annual meeting.

He said negotiators would have to work into the night to secure an agreement to be put to the 48 member countries of the regional development bank. An agreement has to be reached Sunday or Monday morning at the latest, or the capitalization could be postponed for months, Bernardo said.

A spokeswoman for the U.S. Treasury declined comment for this article as negotiations are ongoing.

The IDB has ramped up spending in recent years to offset some of the effects of the global financial and economic crisis, and is now facing something of a capital crunch. Without fresh funding from the member countries, its ability to lend will drop significantly in coming years, and loans to the region would dry up.

Speaking to reporters earlier, Oscar Ivan Zuluaga, Colombia's finance minister and currently the chairman of the IDB's board of governors, said technical teams would work through the night to prepare a new document to be presented Sunday, which he hoped would be approved by the members by Sunday afternoon.

The U.S., which is the largest single IDB shareholder with a 30% stake, has laid down 13 conditions, of which six have already been implemented and five are "acceptable," said Bernardo, adding that they are mainly related to improving transparency of the IDB and the speed with which it makes decisions.

However, two of them are "a serious problem," and have been broadly rejected by most of the IDB's other members, Bernardo said. Nevertheless, the minister, who is Brazil's representative on the IDB board of directors, acknowledged that there appeared to be some flexibility in the U.S. position.

One condition would essentially transfer the oversight role played by the International Monetary Fund to the IDB, which would be required to set fiscal targets for those countries which don't have an agreement with the IMF, Bernardo said. Countries would have to meet those goals to be able to borrow from the IDB, he said.

"The IDB has never played that role. We don't think it's appropriate," Bernardo.

Another condition which Bernardo explained would appear to essentially require the IDB to adopt U.S. environmental standards. Bernardo said U.S. directors on the IDB board are free to vote against projects on environmental grounds, but the IDB's standards have to be upheld.

"The bank has to have concerns about environmental sustainability but that has to be negotiated with the countries," Bernardo said.

Within that item, there is also a proposal that two new committees be created to filter projects, Bernardo said, adding that he was willing to examine this particular issue. There's criticism that the new committees would delay the decision-making process, and would effectively have the final say on projects, instead of the board of directors, he said.

Meanwhile, there's still some level of disagreement over the amount of capital to be injected into the IDB, the minister said. The U.S. is proposing that the capital be increased by $60 billion, Bernardo said, which is below the $100 billion initially supported by Brazil and also still below the $80 billion figure around which most members, including Brazil, have now coalesced.

Not all of that has to be paid in to the IDB's coffers, as most is simply committed as a guarantee against which the IDB can borrow money to finance its lending. The current negotiations suggest that 3% of the new capital would be paid in.

Using the U.S. proposal, the U.S. would have to pay in around $1.8 billion and Brazil would have to pay in about $600 million.

The minister sought to separate some other issues which further muddy the waters. While there is plenty of valid criticism of the IDB's role and operations, including from Brazil, that should be a different discussion from the capitalization process, he said.

Moreover, now's not the moment to discuss rearranging the membership quotas within the IDB, he said, as none of the existing members are willing to reduce their participation in the bank.

There has been some speculation that China, for instance, might be willing to make a major investment in the IDB; but that would require one or more of the existing members to cede some of their shares.

(Paul Kiernan contributed to this report.)

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