Thousands of riot police have been deployed in the Pakistani city of Lahore, to prevent any disruption to a planned mixed-sex mini-marathon.
Islamists say the protests will continue
Islamic activists are demanding that women do not take part in the race, as they say that such activities run counter to Islam.
Police arrested at least 160 people on Friday in clashes with protesters.
This is the second time Lahore has held an international marathon. Some 15,000 runners are expected to take part.
Organisers say they want to promote a culture of tolerance and moderation in Pakistan.
'Against our culture'
"We will not allow anyone to disrupt it," Lahore police chief Amir Zulifquar said on Saturday, the Associated Press news agency reports.
He said some 6,000 officers would be on duty on Sunday to maintain order.
The six-party alliance of religious parties, the MMA, say they will go ahead with protests.
"It is against our cultural, social and religious norms," Liaquat Baluch of the MMA said.
"We will protest if they hold it."
On Friday police fired tear gas shells and resorted to a baton charge in and around the premises of the Islamiya College in Lahore.
The protesters insist women runners should race separately, and indoors.
The man supervising the race logistics for the provincial government, Ghaus Akbar, has said that "foolproof police arrangements will be in place to ensure the safety of the participants".
Women and men staged a "symbolic mini-marathon" last May
Organisers hope the race will help raise funds for the victims of the earthquake which devastated parts of northern Pakistan and Kashmir in October.
Last year's marathon in Lahore was the first time Pakistan had staged such an international event. It passed peacefully even though women took part.
But last April a ban on mixed gender races was enforced after Islamic hardliners attacked runners in a race in the city of Gujranwala, about 100km (60 miles) north of Lahore.
In May women's rights activists defied the ban by holding a symbolic one kilometre "mini-marathon" in Lahore. Women participants wore traditional dress, the salwar kameez, and some wore high heels rather than running shoes.