Thousands of Ahmadiyya Muslims are expected to descend on the Baithul Futuh Mosque in Morden as Eid al-Fitr celebrations get underway today.
Heavy traffic has been reported between Rose Hill in Sutton and the mosque in London Road, Morden, as up to 15,000 worshippers travel to the mosque to mark the end of Ramadan.
The Eid celebrations are expected to include a message of peace from the movement's leader, His Holiness Hadhrat Mirza Masroor Ahmad, four days after three Ahmadis were reportedly murdered for their beliefs in a mob attack in Pakistan.
A grandmother and her two granddaughters, aged seven and eight months, were killed by extremists targeting Ahmadise in the town of Gujranwala in Punjab, it has been reported.
Houses were looted after a mob gathered outsides the properties claiming an Ahmadiyya Muslim had posted a picture of the Ka'abah on Facebook, an allegation denied by Ahmadis.
A spokesman for Ahmadiyya Muslim Association UK (AMA UK) said a pregnant mother has suffered a miscarriage and eight other women and children are being treated for burns and sever injuries following the attack.
London has become the centre of the Ahmadiyya community, with thousands of members fleeing Asian, African and Arab countries where they have faced persecution for their beliefs.
Pakistani law dictates Ahmadi can be imprisoned for three years and even sentenced to death for claiming to be Muslims.
Rafiq Hayat, national president of AMA UK, said: "A lot of families are in shock. You know when you are gearing up for a big celebration like Christmas and something tragic happens and a family dies on Christmas Eve, it's like that."
AMA UK is now calling on the British government to raise concerns over the safety of Ahmadais with Pakistan.