SAO PAULO (Reuters) - President Luiz Inacio Lula da Silva said on Friday that Brazil would react to U.S. President Donald Trump's decision to issue tariffs on steel imports, suggesting his government could file a complaint at the World Trade Organization, or tax U.S. products.

"I hear they are now going to tax Brazilian steel. If they do it, we will react commercially, either by filing a complaint to the WTO or taxing products we import from them," Lula said in a radio interview.

The South American country is one of the largest sources of U.S. steel imports. Trump earlier this week substantially raised tariffs on steel and aluminum imports to a flat 25% "without exceptions or exemptions".

Lula's remarks point to a more aggressive approach to the tariffs than his economic team had suggested in previous statements. Both his finance and trade ministers called for dialogue and potential negotiations with the United States.

The White House in a fact sheet on Thursday - when Trump moved to scrap decades-old low tariff rates, raising them to match those of other countries - also pointed to Brazil's ethanol tariffs as an example of unfair trade practices.

Lula said he wants Brazil's relations with the U.S. to be "harmonious" and noted the two countries have balanced trade, but added: "If there is any action against Brazil, there will be reciprocity."

The U.S. has run a trade surplus with Latin America's largest economy since 2008, which reached $253 million last year on more than $80 billion of bilateral trade.

The Brazilian leader said he was worried about Trump's "protectionism", saying it goes against the United States' long-standing defense of free markets.