Twitter says it will no longer "amplify" tweets by state-controlled media organisations, by excluding them from its recommendation systems.
The move makes affected accounts less likely to appear in search results, notifications and on a user's timeline.
The company will also label the accounts of government-linked media, as well as "key government officials" from China, France, Russia, the UK and US.
Russia's RT and China's Xinhua News will both be affected by the change.
Twitter said it was acting to provide people with more context about what they see on the social network.
Other social platforms, including video-sharing giant YouTube, already label the channels of state-backed media organisations.
Twitter will label media organisations "where the state exercises control over editorial content through financial resources, political pressure or control over production and distribution".
Editors and senior staff will also have their accounts labelled.
However, publicly funded news organisations with editorial independence will not be labelled, including the BBC and the US network NPR.
Twitter says it will label key government officials, including foreign ministers, institutions, ambassadors and spokesmen and women from the five permanent members of the UN Security Council: China, France, Russia, the UK and US.
"Our focus is on senior officials and entities that are the voice of the nation state abroad," Twitter said.
However, politicians' personal accounts will not always be labelled.
For example, President Trump's popular Twitter account @realDonaldTrump will not be labelled, while his official account @Potus will be identified.
Explaining the decision, Twitter said personal accounts "enjoy widespread name recognition, media attention, and public awareness".
Twitter said it would expand the list of labelled accounts and include additional countries over time.