THREE Asian men gained entry to a synagogue on Tuesday - and claimed they only wanted to learn about Judaism and "make peace".
Suspicious members of the Machzikei Hadass Synagogue called the police after the men entered the building in Northumberland Street around 3pm.
When the police arrived, they asked the trio to leave.
A synagogue spokesman said: "We have all been warned to be vigilant.
"The doors now have locks on them which can only be opened by entering a number. "We have been told to make sure nobody else comes in with us when we open the door and to challenge anyone for identification if we do not recognise them."
A poster is now on the notice board, urging members to "stay safe and protect everyone else".
A Greater Manchester Police spokesman said: "There is a suggestion that the men were there to learn about Judaism. But we are unsure whether that is the case."
Police added that no criminal offence had been committed.
A CST spokesman told the Jewish Telegraph: "This incident shows the importance of controlling access to our communal buildings."