The new ad policy at Twitter applies to paid messages that identify political candidates or advocate regarding legislative issues of national importance.

The tightened ad policy included requiring photos and valid contact information, and prohibited state-owned media or national authorities from buying political ads to be shown on Twitter outside their home countries.

Those placing these Twitter ads will need to be "certified" by the company and meet certain guidelines, and the ads will be labeled as political "issue" messages.

"The intention of this policy is to provide the public with greater transparency into ads that seek to influence people's stance on issues that may influence election outcomes," Twitter executives Del Harvey and Bruce Falck said in a blog post.

The new ad policy came as major technology firms including Facebook, Google and Twitter battle against misinformation campaigns by foreign agents.

Facebook, Twitter, Google and Microsoft recently blocked accounts from Russian and Iranian entities which the companies said were propagating misinformation aimed at disrupting the November US elections.

The new ad policy at Twitter applies to paid messages that identify political candidates or advocate regarding legislative issues of national importance.

Examples of issue topics provided by Twitter included abortion, civil rights, climate change, guns, healthcare, immigration, national security, social security, taxes and trade.

The policy did not apply to news agencies reporting on candidates or issues, rather than advocating outcomes, according to Harvey and Falck.

Silicon Valley executives are set to take part in a September 5 Senate hearing about foreign efforts to use social media platforms to influence elections.