ISLAMABAD (Reuters) - The party of slain former prime minister Benazir Bhutto on Wednesday decried what it called “pre-poll rigging” ahead of Pakistan’s July 25 election, saying the reopening of a criminal case against its co-chairman was politically motivated.

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The Pakistan Peoples Party (PPP) also said men identifying themselves as military officers had pressured some of their candidates to switch affiliation to a “King’s party”, a common euphemism for one favored by the powerful military.

The PPP’s allegations, which come after similar complaints made by former prime minister Nawaz Sharif, marked its first open criticism of the electoral process.

A federal investigation agency this week summoned PPP co-chairman Asif Ali Zardari for questioning in a money laundering case allegedly involving 35 billion rupees ($350 million). Zardari is the widower of two-time prime minister Bhutto, who died in a 2007 suicide attack while campaigning.

The PPP decried the money laundering investigation as political, saying the case was three years old.

“It has been dragged out of cold storage two weeks before an election as a clear case of political victimization and can be classified as pre-poll rigging,” the PPP statement said.

It also named people who identified themselves as military officers and who had been “pressuring our party members and supporters to switch to the King’s party”.

The PPP’s statement did not specifically name the “King’s party”.

The accusations echo those made by Sharif, who was convicted of corruption last week. He has said elements of the military are trying to deny his Pakistan Muslim League-Nawaz (PML-N) a second term in office.

Sharif, who was removed from office by Supreme Court order last year over an investigation into his family’s vast wealth, was convicted on corruption charges last week by an anti-graft court.

He is expected to be arrested when he returns to Pakistan on Friday to face his seven-year sentence.

Dozens of PML-N activists were arrested this week and appeared in court on Wednesday, accused of plotting unrest to coincide with Sharif’s return

Pakistani cricket hero-turned-politician Imran Khan, the presumptive leader in the elections, has rejected talk of any pre-poll meddling, saying the two other major parties know they are losing because Pakistanis are sick of corruption.

Responding to Sharif’s accusation, army spokesman Maj. Gen. Asif Ghafoor said on Tuesday: “We don’t have a political party. We don’t have a loyalty.”

Sharif has also said the military’s intelligence wing, the Inter-Services Intelligence agency (ISI), is intimidating his party’s candidates to switch loyalties, or to run as independents.