KABUL, Afghanistan — A suicide bomber struck an election rally in Afghanistan's eastern Nangarhar province on Tuesday, killing at least 14 people and wounding around 40, a provincial official said.

The attack, the first since campaigning began last week ahead of elections for the lower house of parliament, underscored the widespread violence gripping the country 17 years after the US-led invasion toppled the Taliban.

The vote is scheduled for Oct 20 but it's unclear if the balloting will go ahead in areas controlled by the Taliban, who have seized several districts across the country in recent years and who carry out near-daily attacks.

Tuesday's attack targeted a rally for Abdul Naser Mohmand, an independent candidate, who was unharmed.

"Most of the people killed or wounded are elders who had gathered for the campaign rally," said Attahullah Khogyani, a spokesman for the provincial governor. He said some of the wounded were in critical condition, indicating the death toll could rise.

No group immediately claimed responsibility for the attack, but both the Taliban and an Islamic State affiliate are active in the province and opposed to elections.

In a separate attack, at least seven children were wounded when a bomb went off near a cricket pitch elsewhere in Nangarhar, Khogyani said. The wounded children were all 10 to 14 years old, he added.

The U.N. mission to Afghanistan condemned the attack on the rally and expressed concern about violence around the election campaign.

"I am outraged by attacks deliberately targeting civilians seeking to exercise their basic right to participate in elections," said Tadamichi Yamamoto, the U.N. envoy to Afghanistan. "This violence, including today's reprehensible attack in Nangarhar, is an assault on the constitutional rights of the people of Afghanistan." The election campaign kicked off last Friday with 2,565 candidates vying for seats in the 249-member chamber, including 417 women candidates.

In the run-up to campaigning, five candidates were killed in separate attacks. Officials from the country's Independent Election Commission said another two candidates have been abducted, with their fates unknown, and that three others have been wounded in attacks. Afghan security forces killed three bodyguards of an independent candidate during a raid on a house near his residence in the eastern Kunar province on Sunday.

A number of political parties and opposition groups have expressed concerns over the transparency of the vote, leading to demands that a biometrics system be used to register voters — a first in Afghanistan's history.

Afghanistan's parliament includes a lower and an upper house, but only members of the lower house are directly elected. The upper house consists of parliamentarians chosen from local councils and those appointed by the president, as well as members elected in district elections.

Afghan forces have struggled to combat the Taliban and IS in recent years, suffering heavy casualties and withdrawing from many rural areas.

Security forces battling insurgents in the southern Helmand province were struck by an errant NATO airstrike on Monday, which killed four police, a soldier and an intelligence agent, according to Ghafor Ahmad Jawad, a Defense Ministry spokesman. He said another 20 Afghan forces were wounded in the friendly fire incident.

AP