LONDON (Reuters) - Fitch has become the second top rating agency to warn that the prized triple-A credit scores of the World Bank and other top multilateral lenders will be hit if Donald Trump withdraws U.S. support for them.

The U.S. president signed an Executive Order last week for a six-month review of government support to all international intergovernmental organisations to decide whether it should withdraw from them or seek reform.

"Any signal that a withdrawal from an MDB (multilateral development bank) has become a real possibility could lead to negative rating action," Fitch said, a day after Moody's delivered the same warning.

Fitch said it still viewed withdrawals by the U.S. as "unlikely" but said the impact - if it were to do so - would be considerable, causing financial damage, and that it could also "set a precedent and affect the cohesion of remaining shareholders".

The rating firm added that the immediate reaction would likely be to put the impacted MDBs' rating on a downgrade warning - or "Rating Watch Negative" in rating agency terminology.

Whether they were then stripped of their triple-A scores, "would depend on the conditions of the withdrawal and the response by other shareholders", Fitch said.