Google admitted on Monday it had found evidence that Russian operatives attempted to meddle in last year's US presidential election by spending tens of thousands of dollars on politically divisive advertisements across its platforms.

Sources from within Google, a unit of Alphabet Inc, told the Washington Post and Reuters news agency that it was investigating attempts by Kremlin affiliates to abuse its systems and spread disinformation.

Read more: Facebook, Russia and the US elections - what you need to know 

A spokesperson for Google said the company was "taking a deeper look to investigate attempts to abuse our systems, working with researchers and other companies," and that it would "provide assistance to ongoing inquiries."

Google, the online giant and one of the world's largest advertising businesses, said it had "a set of strict ads policies including limits on political ad targeting and prohibitions on targeting based on race and religion."

Silicon Valley as a battleground

Google's admission comes just a week after Facebook, the world's largest social network, revealed that a Russian internet agency last year purchased around 3,000 targeted advertisements aimed at influencing the presidential election, which saw Republican Donald Trump defeat his Democratic rival Hilary Clinton.

According to sources at Google, the ads on its various platforms, which include Gmail, YouTube and its Double Click ad network, were not purchased by the same Russian entity that bought the ads on Facebook.

Facebook, along with Twitter, alleges that its ads were purchased by a Kremlin-affiliated content farm known as the Internet Research Agency, based in St. Petersburg. According to lawmakers and researchers, the company employs hundreds of "trolls" to post fake or discredited content from phony social media accounts posing as US or European citizens. A study by the Oxford Internet Institute, which is affiliated with the British Oxford University, found that current and former US military personal were especially targeted by the Russian disinformation campaigns.

Later on Monday, Microsoft said it was investigating whether it too had been targeted.

Tech firms to appear before investigation committees

Facebook has handed over the contents of the ads to congressional investigators probing Moscow's alleged meddling in the election, as well as potential collusion between Kremlin officials and members of the Trump campaign team.

Read more: What you need to know about the five inquiries looking into Donald Trump, James Comey and Russia

Representatives from all three internet companies are expected to appear before an open Senate Intelligence Committee on November 1, as evidence continues to mount that their platforms were manipulated with the aim of steering Trump towards winning the presidency. Google, however, is the only company that has yet to confirm that it will appear.

Silicon Valley's tech giants have come under increasing scrutiny from lawmakers amid revelations that they may have helped last year's presidential election. Democratic lawmakers are reportedly planning to introduce new legislation that would require internet companies to publically disclose more information about political ad purchases on their platforms.

dm/bk (Reuters, AFP)