Scores of people wounded in a horrific suicide attack at a volleyball game in eastern Afghanistan were flown to hospital in Kabul, officials said Monday, as families mourned 50 killed in the blast.

In the country's deadliest single attack since 2011, the bomber detonated his explosives among packed crowds watching a tournament featuring three local teams in the volatile province of Paktika.

The bloody attack underlined the challenges facing President Ashraf Ghani, who came to power in September, as US-led NATO troops wind down operations and Afghan security forces take over responsibility.

Ghani was among those who visited victims being treated for wounds at a 400-bed military hospital in the Afghan capital.

Many of the wounded were children and young men, wrapped in bloody bandages.

"Last night 54 people wounded by the terrorist action in Paktika were transferred by military helicopter to the Sardar Mohammad Daud Khan hospital (in Kabul)," Zahir Azimi, spokesman for the defence ministry, said via Twitter.

There was no immediate response from the Taliban, but the insurgents often distance themselves from attacks that claim mostly civilian lives.

The blast, in the Yahya Khail district of Paktika, came at about 5:00 pm (1230 GMT) as hundreds of people had gathered to watch the volleyball, a popular sport among young men in Afghanistan.

"I and my friends were watching the game and we were cheering each time our team scored," Abdulhay, an 11-year-boy being treated in hospital in Sharana, the provincial capital of Paktika, told AFP by telephone.

Paktika, one of the most restive provinces in Afghanistan, borders Pakistan's lawless tribal areas, where many insurgent leaders seek safety from NATO and Afghan forces.

President Ghani condemned the attack as "inhumane and un-Islamic". He added: "This kind of brutal killing of civilians cannot be justified."

Pakistani Prime Minister Nawaz Sharif also denounced the bombing and vowed to fight the "terrorism that is the common enemy of both countries".

One witness, Khushal, 25, told AFP that he saw a man in a traditional shawl get off his motorbike before blowing himself up.

Paktika was also hit by a massive suicide blast in July, when a bomber driving a truck packed with explosives killed at least 41 people at a busy market in Urgun district.

In April last year, 46 people, including 36 civilians and 10 troops and police, were killed in a Taliban attack against the law court in the western province of Farah.

A suicide blast at a shrine in Kabul on the Shiite holy day of Ashura in December 2011 killed 80.

Sunday's attack occurred on the same day that the lower house of parliament approved agreements to allow about 12,500 NATO-led troops to stay on next year.

US-led NATO combat operations will finish at the end of this year, but the Taliban have launched a series of offensives that have severely tested Afghan soldiers and police.

The new NATO mission -- named Resolute Support -- will focus on supporting the Afghan forces, in parallel with US counter-terrorism operations.

But fears are growing that Afghanistan could tip into a cycle of violence as the US military presence declines, with the national security forces already suffering huge casualties on the battlefield.

The army and police suffered 4,634 fatalities in combat to the beginning of November this year, on top of 4,350 killed during 2013, according to the US military.

Police said they were investigating a blast in Kabul on Monday that wounded four civilians.

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