Malaysian police have used tear gas and water cannon to disperse thousands of people gathering to demonstrate against a security law allowing detention without trial.
"There was no violent confrontation coming from the protesters but they were tear-gassed and dispersed," Al Jazeera's Harry Fawcett, reporting from Kuala Lumpur, said.
"They have been swiftly and pretty heavily dealt with."
The protesters had planned to march towards the national palace, but scores of people were reportedly detained even before they had reached the rally.
Before the march started, Muhammad Sabtu Osman, the Kuala Lumpur police chief, said that 150 people - identified as protesters because they were wearing opposition t-shirts and headbands - had been detained to prevent them from taking part.
"This is not reasonable. It's prayer time and this action is a breach of our religious freedom and duty," she said.
"The position of the police and the government is to ensure that nothing untoward happens with certain groups that want to exploit the situation for their own political reasons," he said.
"That is something we will not tolerate ... whether you are for or against the ISA."
كُنتُمْ خَيْرَ أُمَّةٍ أُخْرِجَتْ لِلنَّاسِ تَأْمُرُونَ بِالْمَعْرُوفِ وَتَنْهَوْنَ عَنِ الْمُنكَرِ وَتُؤْمِنُونَ بِاللَّهِ ۗ Kamu (wahai umat Muhammad) adalah sebaik-baik umat yang dilahirkan bagi (faedah) umat manusia, (kerana) kamu menyuruh berbuat segala perkara yang baik dan melarang daripada segala perkara yang salah (buruk dan keji), serta kamu pula beriman kepada Allah (dengan sebenar-benar iman). (Surah Ali `Imran: 110)