"Based on briefings we have received, we have concluded that the Russian intelligence agencies are making a serious and concerted effort to influence the US election," Senator Dianne Feinstein, vice chairman of the Senate Intelligence Committee and Congressman Adam Schiff ranking member of the House Intelligence Committee said.
"At the least, this effort is intended to sow doubt about the security of our election and may well be intended to influence the outcomes of the election - we can see no other rationale for the behaviour of the Russians," the two lawmakers said in a joint statement.
"We believe that orders for the Russian intelligence agencies to conduct such actions could come only from very senior levels of the Russian government.
"We call on President Vladimir Putin to immediately order a halt to this activity. Americans will not stand for any foreign government trying to influence our election. We hope all Americans will stand together and reject the Russian effort," they said.