Officials of the White House, speaking anonymously as the matter was still on an ongoing investigation, said that hackers have breached the unclassified portions of the computer networks of the White House over the recent weeks.
The security breaches have caused temporary disruptions to certain services of the network as cybersecurity experts attempted to repel the attack.
According to the sources, the hackers are thought to be in alliance with the government of Russia.
The attempted hacks, however, have not caused any damage to White House's systems. In addition, there are no signs that the classified portion of the network has been breached.
"In the course of assessing recent threats, we identified activity of concern on the unclassified Executive Office of the President network," said an official of the White House.
"We took immediate measures to evaluate and mitigate the activity. . . . Unfortunately, some of that resulted in the disruption of regular services to users. But people were on it and are dealing with it."
Currently working on the investigation are the Secret Service, the FBI and the National Security Agency.
The security breach was alerted to White House officials by an ally, the sources added, which was discovered less than a month ago. Several White House staff members were immediately requested to change their login passwords, and access to the Intranet and VPN was temporarily turned off.
The Department of Homeland Security said separately that it will be increasing the security measures placed on several federal buildings located in Washington and in major cities in the country after terrorist organizations continue to make threats and the recent terrorist attack on the Parliament of Canada.
There has been an increase in the activities of hackers from Russia recently, including the massive cyberattack that JPMorgan Chase revealed targeted 76 million households.
While the method of the attack and its motive remains unclear, reports reveal that intelligence officials for the United States believe that the perpetrators of the attack were from Russia.
The hackers, which were able to extract names and contact details of account holders in JPMorgan, are also believed to have "at least loose connections" with Russian government officials.
A group of Russian hackers, dubbed the Sandworm Team, have also recently been exposed for taking advantage of the vulnerability in the Windows operating system that has allowed the team to carry out cyberespionage on both organizations and countries, including NATO, Ukraine, and other foreign governments.
According to security firm iSIGHT Partners, the Sandworm Team had been running the campaign for the previous five years.