A bomb exploded on Friday inside a mosque in eastern Afghanistan, seriously wounding a candidate in upcoming parliamentary elections and at least 16 other people, an official said.

The candidate, Mawlvi Saydullah, was making a speech inside the mosque in Mando Zayi district when the blast went off, shattering windows. His bodyguard and at least 15 other civilians were also hurt, said Mubariz Zadran, spokesman for the provincial governor.

“He was the target,” Mr. Zadran said, referring to Mr. Saydullah.

Afghanistan is due to hold national parliamentary elections in September despite fears that a surge in Taliban militant attacks and fighting with international forces could undermine security for the vote.

Meanwhile, military and government officials said on Friday several Taliban figures, including a former spokesman for the insurgents, have been captured in raids by coalition and Afghan forces across the country.

Abdul Hay Motmaen, a spokesman for the Taliban when they ruled Afghanistan, was among those arrested in operations Thursday night in two villages in Andar district of the eastern province of Ghazni, district chief Shir Khan Yosoufzai said.

The international forces in Afghanistan say they have captured more than 100 senior Taliban figures since April in near—nightly raids targeting the top leaders. However, the successes have not managed to reduce insurgent attacks.

In Kandahar in the south, a joint Afghan and coalition force captured a senior Taliban commander who directed the movement of fighters and equipment through Nad Ali district in neighbouring Helmand province, NATO said. The Thursday night operation came a day after a joint force captured a Taliban logistics officer for Taliban networks operating in Kandahar city, the coalition said.

In the east, Afghan and coalition forces captured an insurgent suspected of making bombs Thursday night in Nangarhar province.

The security force targeted a compound outside the provincial capital Jalalabad in pursuit of the man, and Afghan forces used a loudspeaker to call for all occupants to peacefully leave the buildings. After the occupants were interviewed, one of them led the security force to a different compound where the bomb—making suspect was apprehended.

On Monday, Afghan and coalition forces killed five insurgents and detained five more near Tatang in Nangarhar. The combined force found multiple automatic weapons along with dozens of rocket propelled grenades and boosters, hand grenades and 2,000 rounds of ammunition.

NATO also reported that an Afghan intelligence unit found materials in a rock quarry in the Spin Boldak district of Kandahar that could have been used to make more than 100 roadside bombs. The cache discovered on Thursday night included 4,200 pounds (1,900 kilograms) of ammonium nitrate, more than 5,400 electronic fuses, 3,200 yards (meters) of detonation cord and 600 pounds (275 kilograms) of black powder.

NATO is hoping that seizing weapons and key insurgent leaders will weaken the Taliban’s operational capacity, while increased patrols by Afghan and coalition troops will bring greater security to areas of the south that have been dominated by the insurgency.

However, the strategy has yet to succeed in reducing violent attacks, which some estimate are at the highest level since early in the nearly nine—year—old war. The Taliban have met the coalition’s stepped—up raids and patrols with a wave of bombings and assassinations.

In Uruzgan province, the Taliban shot and killed the head of the Khas Uruzgan district development council and his assistant on Thursday night as they were leaving a house, district chief Gulab Khan said.

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