At least 133 people have been killed, including a parliamentary candidate, and more than 230 wounded in two separate election-related bombings in Pakistan on July 13, authorities say, amid growing tensions over the return and arrest of ousted Prime Minister Nawaz Sharif, who is facing corruption charges.

Pakistani police said a suicide bomber struck a campaign convoy near the southwestern city of Quetta, the capital of Balochistan Province, killing at least 128 people, including Siraj Raisani, a candidate running in the July 25 general elections. At least 200 people were wounded in that attack, which was claimed by the Islamic State (IS) terror group.

Home Secretary Haider Ali Shikoh confirmed that Raisani, who was a member of the Balochistan Awami Party, had died. IS claimed responsibility for the attack in an announcement by the militant group's Amaq news agency.

Earlier in the day, five people were killed and at least 32 were wounded in a bomb blast targeting another candidate. No one claimed responsibility for that attack.

The blast targeted a convoy transporting former Housing and Works Minister Akram Khan Durrani, who escaped unharmed, local police chief Khurram Rashid said.

The U.S. State Department in a statement late on July 13 strongly condemned this week's attacks on political candidates and their supporters in Pakistan.

"These attacks are cowardly attempts to deprive the Pakistani people of their democratic rights," it said. "We will continue to stand with the people of Pakistan and the broader South Asia region in their fight against terrorism."

With violence escalating, Pakistan's army said earlier this week that it plans to place 371,000 soldiers around polling stations to ensure the elections are "free and fair."

Durrani is a candidate for Muttahida Majlis-e Amal, an election alliance of radical religious groups.

Police said Durrani was on his way to address a campaign rally in the northwestern town of Bannu when a bomb planted on a motorcycle detonated.

WATCH: Blast Targets Pakistan Election Candidate

Durrani is running as a candidate for Bannu in the July 25 general election.

Speaking to reporters after the attack, Durrani said authorities had warned him about potential security threats.

"I remain safe but four of my allies have been martyred," he said, adding that he did not know who was behind the attack.

Durrani visited hospitals tending to the wounded, many of whom are party supporters.

Former cricket star Imran Khan, whose Pakistan Tehrik-e Insaf party is gaining ground in opinion polls ahead of the elections, condemned the attack.

"There seems to be a conspiracy to sabotage the 25 July elections but the people of Pakistan will not allow any design intended to target these historic elections to succeed," Khan wrote on Twitter on July 13.

Durrani is the leader of Jamiat Ulema-e Islam, a hard-line religious party. He was the former chief minister of Khyber Pakhtunkhwa, the restive province in northwest Pakistan that borders Afghanistan.

No one claimed responsibility for the July 13 attacks, but it came after a suicide bomber attacked a crowd waiting for an election rally organized by the secular Awami National Party (ANP) in the northwestern city of Peshawar on July 10.

The Pakistani Taliban claimed responsibility for the July 10 attack that killed 20 people, including Haroon Ahmed Bilour, a candidate for a seat in the provincial legislature. Another 65 people were wounded.

Meanwhile, Sharif was arrested upon arrival in the eastern city of Lahore after flying back from London to face a 10-year prison sentence on corruption charges. He was accompanied by his daughter Mariam. The two were in London visiting Sharif's ailing wife when a Pakistani court convicted them of corruption. Mariam, who was sentenced to seven years in prison, was also arrested.



Sharif's son-in-law is currently serving his one-year prison sentence on the same charge, which stems from the purchase of luxury apartments in Britain that the court said were bought with illegally acquired money.

Sharif is expected to appeal his conviction and seek bail.

With reporting by AP, Reuters, and The Tribune