Fighting between the Taliban and Afghan government forces resumed Sunday in the restive southern province of Helmand, officials said, ending a three-day ceasefire agreed by the warring sides to mark the Eid al-Fitr holiday.

There were clashes on the outskirts of Lashkar Gah, the capital of Helmand, which has seen intense fighting since the United States began its final troop withdrawal from Afghanistan on May 1, an Afghan military spokesman and a local official said.

"The fighting started early today morning and is still ongoing," Attaullah Afghan, head of the Helmand provincial council, told AFP.

He said Taliban fighters attacked security checkpoints on the outskirts of Lashkar Gah and other districts.

An Afghan army spokesman in the south confirmed fighting had resumed.

The three-day truce initiated by the Taliban and swiftly agreed to by the Afghan government had largely held during the Eid holidays that ended last night.

At least 12 people were killed at a mosque outside Kabul, however, by a bomb blast claimed by the jihadist Islamic State group.

Before the ceasefire, violence had surged in several provinces of Afghanistan -- including former insurgent bastions Helmand and Kandahar.

IS claims mosque bombing

The jihadist Islamic State claimed it carried out this week's attack on a mosque on the outskirts of the Afghan capital that left 12 worshippers dead, SITE Intelligence Group reported.

The explosion happened inside a mosque in Shakar Darah district of Kabul province during Friday prayers and shattered the relative calm of a three-day ceasefire agreed between the Taliban and the Afghan government.

IS said its fighters had placed an explosive device inside the mosque and detonated it after worshippers arrived to offer prayers on the second day of the Eid al-Fitr holidays, the US monitor of jihadist groups said late Saturday.

The bombing killed the imam of the mosque, who was leading the prayers.

Friday was also the second day of a three-day ceasefire agreed by the Taliban and the government to mark Eid al-Fitr.

The ceasefire ended late on Saturday and so far no fighting between the two warring sides has been reported.

The temporary truce was announced after soaring violence since May 1, when the US military began formally withdrawing its last remaining troops from the country.

A series of blasts outside a girls' school in Kabul last week killed more than 50 people and wounded scores, most of them female students.

No group has so far claimed the attack, one of the deadliest in recent years.

In recent weeks, fighting between the Taliban and government forces had surged across several provinces before the ceasefire was agreed, including in the southern provinces of Kandahar and Helmand.