"On Friday night, August 21, the Open State Foundation was informed by Twitter that it suspended... Access to Diplotwoops and all remaining Politwoops sites in 30 countries," said the Open Foundation, which started Politwoops in the Netherlands in 2010.
Twitter switched off Politwoops in the United States in May and the Open Foundation voiced fears it may happen elsewhere.
Twitter ended the US website's access to its API (application programme interface) which allowed it to see when a politician deleted a tweet, often an indicator they have changed their mind or realised a mistake.
It started operating in the US in 2012 thanks to the Sunlight Foundation, which fights for transparency in politics.
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Diplotwoops which screens deleted messages by diplomats and embassies around the world was set up in 2014.
Twitter was not immediately available for comment, but the Open Foundation said it was told the social media giant decided to suspend access to Politwoops "following thoughtful internal deliberation and close consideration of a number of factors that doesn't distinguish between users."
Open Foundation director Arjan El Fassed insisted comments made by politicians on Twitter should remain in the public domain.
"What elected politicians publicly say is a matter of public record. Even when tweets are deleted, it's part of parliamentary history," he said.
"What politicians say in public should be available to anyone."
"This is not about typos but it is a unique insight on how messages from elected politicians can change without notice," El Fassed added.