LAHORE, Pakistan/ISLAMABAD (Reuters) - Pakistani authorities have opened a criminal investigation into leaders of jailed former Prime Minister Nawaz Sharif’s political party under an anti-terrorism law, 10 days before a hotly contested general election, according to police documents.

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The case relates to a march staged by the Pakistan Muslim League-Nawaz (PML-N) on July 13, when Sharif returned to Pakistan, which defied a ban on holding public rallies on a Friday. The former premier was arrested minutes after landing in the country after being sentenced in absentia by an anti-corruption court on July 6.

Copies of two separate First Information Reports (FIR), which mark the formal opening of a criminal investigation, named PML-N leader Shehbaz Sharif, who is Nawaz Sharif’s brother, and a number of other key figures. They include former Prime Minister Shahid Khaqan Abbasi, who replaced Sharif last year and served until June, when the caretaker government took over.

The FIRs cite section 7 of the Anti-Terrorism Act, which has broad provisions defining terrorism to include creating public fear, and lists 10 alleged violations of ordinary criminal law including unlawful assembly.

“We are taking action against PML-N leaders,” the caretaker home minister of Punjab, Shaukat Javed, told Reuters on Sunday. “But no one will be arrested before the elections.”

He said that including the terrorism charges was a “mistake” that would be corrected later.

Shehbaz Sharif led Friday’s march across the city of Lahore, in which tens of thousands of people took part, intending to send a message to rivals that the popular vote is still with the PML-N ahead of the July 25 election.

National polls indicate a close race between the ruling PML-N and the Pakistan Tehreek-e-Insaf (PTI, or Pakistan Justice Movement) led by former cricket star Imran Khan, with the Pakistan Peoples Party in third place.

Sharif, who was removed from office by the Supreme Court last year and sentenced this month to 10 years in prison for corruption, alleges the military is aiding a “judicial witch-hunt” to prevent the PML-N from winning a second term.

The party’s past five years in government have been characterized by discord with the military, which has ruled Pakistan for nearly half its 71-year history.

The Sharifs’ return could shake up an election riven by accusations the military is working behind the scenes to skew the contest in favor of Khan, who describes Sharif as a “criminal” deserving no support.

Musadik Malik, a senior PML-N official and member of the Senate, said the FIRs were part of a pattern that included pressuring candidates to change to PTI and corruption cases against other party leaders.

“This FIR is just another attempt of intimidation and political victimization,” Malik said.

Malik said the PML-N rally was overwhelmingly peaceful and any ban on gatherings so close to the election was unfair.