At least four people were killed and a dozen others injured when gunmen stormed a crowded government building in eastern Afghanistan on Wednesday, following a suicide bombing, with desperate survivors leaping from windows to escape the fighting, witnesses and officials said.

Security forces rushed to the scene after armed men attacked the office in Jalalabad, the capital of eastern Nangarhar province, in the latest violence to hit the war-torn country as it gears up for a presidential election on September 28.

Terrified children at a nearby school climbed over walls to get further away from the fighting.

A provincial spokesman, Ataullah Khogyani, said a suicide bomber had initially detonated explosives, after which the gunmen attacked.

Security forces fought to clear the building for several hours before declaring all three gunmen dead, interior ministry spokesman Nasrat Rahimi said roughly six hours after the attack began.

Witnesses and an AFP reporter could hear gunshots immediately after the initial blast.

One of the centre's employees, Haji Qudrat, described the moment one of the gunmen entered his office. “After the explosion, we heard small gunfire in our corridor, then a man entered our office with a gun and started shooting,” he told AFP from a hospital in Jalalabad, where he was receiving treatment for a wounded leg.

“I jumped out the window. Some of our friends are either killed or wounded.” Qudrat said there had been around 200 people inside the centre when the bomber detonated — 80 employees, and the rest people waiting to receive their national electronic identity cards, or “tazkiras”.

“I was in class when I heard a big explosion followed by intense gunfire,” said Mohammad Ullah, a teacher at a nearby school.

“The kids started crying so we had to vacate the school. We jumped over the walls to take the students to a safer place,” he told AFP.

No group has claimed the attack. Both the Taliban and the militant Islamic State (IS) group are active in Nangarhar, which borders Pakistan.

Door 'open' for talks

The assault came a day after the Taliban killed nearly 50 people and wounded dozens more in two separate attacks — one near a campaign rally for President Ashraf Ghani in the central province of Parwan, and one in Kabul.

The militants have vowed to disrupt the upcoming presidential election, scheduled for September 28, in which Ghani is taking on his own Chief Executive, Abdullah Abdullah, and more than a dozen other candidates.

The winner is hoping for a mandate to negotiate with the Taliban for a lasting peace in the country suffering from decades of violence. But the insurgents want to undermine the legitimacy of the process and keep the president weak.

“We already warned people not to attend election rallies. If they suffer any losses that is their own responsibility,” Taliban spokesman Zabihullah Mujahid said in a statement released after Tuesday's blasts.

They have also promised more violence after US President Donald Trump called off talks earlier this month seeking a deal that would have allowed Washington to begin withdrawing troops from Afghanistan, site of America's longest war.

“The president has made clear that he will not negotiate a peace agreement while the Taliban continues such attacks,” a White House statement condemning Tuesday's blasts said.

But the militants have also repeatedly voiced their belief that the US will eventually have to return to the table for more negotiations. Chief negotiator Sher Mohammad Abbas Stanikzai reiterated that stance in an interview with the BBC hours after Tuesday's attacks, stating “our doors are open for negotiations”.

He also defended Taliban violence during the months of talks, arguing that the Americans had also admitted to killing thousands of Taliban during the discussions.