President Obama issued a stern, thinly veiled warning to Donald Trump against leaking sensitive material he may receive in upcoming classified briefings but said his administration would follow the law and brief both Trump and Hillary Clinton.

"[Clinton and Trump] have been told these are classified briefings," he said. "If they want to be president, they've got to start acting like presidents, and that means being able to receive these briefings and not spread them around."

Asked if he is worried that Trump will do that or has already done so in some capacity, the president demurred.

"Well, I think I've said enough on that," he said.

Shortly before the harsh words for Trump, Obama said his administration would abide by "both the tradition and the law" and provide classified briefings for both presidential nominees, regardless of party.

"If somebody's the Republican nominee for president, they need to get a security briefing [so] if they were to win they are not starting from scratch in terms of being prepared for this office," Obama assured.