CANNES, France (Reuters) -Cannes Film Festival director Thierry Fremaux wants more details before discussing President Donald Trump's proposed tariffs on films made outside the United States, he said on Monday.

Fremaux, speaking to journalists one day before the festival is due to start, was asked what he might say to Trump about a threatened 100% tariff.

"It's quite difficult to answer this question, which is based on the announcement by the American president, who we're getting used to over the last three months saying something and then contradicting himself etc. So I don't know what to say."

Fremaux is not the only one, with many studio executives alarmed and baffled following Trump's statement earlier this month. Few details have been issued about how such a levy would work.

However, Trump's reasoning - that the U.S. film industry is dying a "very fast death" due to incentives that other countries are offering to lure filmmakers - could be a starting point, he said.

"The idea that American cinema would be penalised by foreign countries, I think it's a topic that's worth discussing," he said.

The 78th Cannes Film Festival is due to kick off on Tuesday evening with Amelie Bonnin's comedy "Leave One Day" as the opening feature - the first time the festival has been opened by a first-time filmmaker, according to Fremaux.