SAO PAULO (Reuters) -Shares in Brazilian steelmaker Gerdau rose more than 4.5% on Monday after U.S. President Donald Trump said he planned to announce 25% tariffs on all steel and aluminium imports into the United States.

Gerdau has units in the U.S. and had previously touted its substantial operations in the country as a hedge against the risk of protectionism from Trump.

"Gerdau is typically seen as a key beneficiary in this context," BTG Pactual analysts said, though he said details of the tariffs were uncertain and that U.S. steel fundamentals were under pressure in the short term.

"While the initial reaction may be to cover shorts or look for a quick trade, we recommend some caution," they said.

Gerdau's peer CSN, which is more exposed to the Brazilian market, was up 0.5%, while Usiminas gained 2.5% in an overall positive session for Brazilian equities.

The South American country is one of the largest sources of U.S. steel imports.

(Reporting by Isabel Teles; Editing by Gabriel Araujo and Barbara Lewis)