WASHINGTON (REUTERS) - Republican presidential candidate Donald Trump said on Thursday the disappearance of an EgyptAir plane over the Mediterranean looked like an act of terrorism, making the link before authorities involved in the investigation did so.

Authorities in Egypt and France said it was too soon to say what caused the Airbus A320 carrying 66 people to come down on its way from Paris to Cairo.

In a morning Twitter post, Trump said: "Looks like yet another terrorist attack. Airplane departed from Paris. When will we get tough, smart and vigilant? Great hate and sickness!"

The post came several hours before a Greek warship searching for the jet found two large plastic objects floating in the sea and Egypt's aviation minister said a terrorist attack was more likely to have taken down the aircraft than a technical failure.

Former US Defense Secretary Robert Gates, a Republican who served in Democratic President Barack Obama's administration, said Trump's tweet came too soon before officials had a chance to discover what happened. "It prejudges the outcome," Gates told MSNBC. "It's always better to wait until you act - know what the facts are before you open up. I realise that's a very unusual thing in American politics, but it ought to be tried occasionally."

Obama was briefed on the missing plane and has directed officials to offer US assistance, the White House said.