President-elect Donald Trump could reverse President Barack Obama's executive order and allow Russian intelligence officials back into the United States once he takes office, but that would be inadvisable, a senior US official said on Thursday.

There is no reason to believe Russia will cease interfering in US and other countries' elections, Obama administration officials told reporters on a conference call after the president announced sanctions against Moscow.

"We believe these steps are important because Russia is not going to stop," one official said. "We have every indication that they will interfere in democratic elections in other countries, including some of our European allies," the official aid.