Germany's domestic intelligence agency says some parts of the anti-Covid lockdown movement are being kept under observation amid concerns they may be trying to delegitimise the state.
They are focusing particularly on some members of the "Querdenker" (lateral thinkers) movement and say they do not fit into previous extremist categories.
The BfV agency highlighted links with far-right and other extremist groups.
Lawful protest was being "exploited to provoke an escalation", it warned.
Although the majority of protesters are not seen as extremists, "Querdenker" anti-lockdown demonstrations have drawn support from a variety of groups, including the far-right AfD party, anti-vaxxers and conspiracy theorists.
The BfV (federal office for the protection of the constitution) said the protest organisers' agenda had gone beyond objecting to anti-Covid measures and had been connecting with Reichsbürger (Reich Citizens) and Selbstverwalter (Sovereign Citizens) who reject the authority of the German government and spread anti-Semitic slurs.
Police and journalists have been attacked. Last August demonstrators overcame police to run up the steps of the Reichstag (parliament) building bearing the flag of former imperial Germany - a key Reichsbürger symbol. Recent protests near the Brandenburg Gate have been dispersed after participants ignored police appeals to wear masks and observe social distancing rules:
- The August protest attracted 38,000 people and police used pepper spray as they became outnumbered
- In November 2020, more than 10,000 people defied a ban in protest at plans to give the government more powers during a pandemic
- Last week some 8,000 protesters were dispersed as MPs voted to allow the government to impose an "emergency brake" where infection rates were high.
As the anti-lockdown extremists do not fit into any one definition - far-right, far-left or militant Islamist - intelligence officials have created a special category of "actions that delegitimise the state, thereby threatening the constitution".
The new designation means that domestic intelligence can observe suspects and gather information and data about them.
Last month, the agency designated the far-right opposition AfD a suspected extremist organisation but a court in Cologne demanded the suspension of a surveillance order while the party challenged the move.
Interior Minister Horst Seehofer said earlier this month that the Querdenker movement had become more prepared to use violence. Some authorities, such as Baden-Württemberg and Bavaria in the south, have already placed it under observation.