Mr Trump tweeted that he had shared "facts pertaining to terrorism and airline safety" and wanted Russia to do more against so-called Islamic State.
He met Russian Foreign Minister Sergei Lavrov in the Oval Office last week.
US media said Mr Trump had shared material that was passed on by a partner which had not given permission.
A report in the Washington Post said Mr Trump had confided top secret information relating to an IS plot thought to centre on the use of laptop computers on aircraft.
Mr Trump's move is not illegal, as the US president has the authority to declassify information.
The action drew strong criticism from Democrats and a call for an explanation from his own Republican party.
The US Senate Intelligence Committee has asked the...Read more...