ISLAMABAD — Hundreds of supporters of a key Islamist party in Pakistan began a sit-in protest in the garrison city of Rawalpindi late on Friday after authorities detained dozens to prevent them from holding the rally in Pakistan's neighboring capital, citing security reasons, officials said.

The Jamaat-e-Islami Pakistan party originally issued a call for holding the sit-in near the parliament building in the capital Islamabad to pressure the government to withdraw a substantial increase in electricity costs, which has drawn nationwide criticism. People complain they are getting electricity bills even higher than their salaries.

Naeem-ur-Rehman, who heads the party, told demonstrators in Rawalpindi that he was willing to stage the sit-in, even for weeks. He said police arrested a large number of the party's supporters to prevent them from staging the sit-in in Islamabad.

Authorities say electricity fees have been increased to meet conditions set by the International Monetary Fund during negotiations that led to a staff-level agreement for a new $7 billion loan deal for Pakistan earlier this month.