The explosion comes as Afghan security forces have been suffering scores of casualties in heavy fighting with Taliban militants in two provinces. In Ghazni province, at least 25 Afghan elite commandos were reported dead.
A suicide bomber blew himself up in the Afghan capital of Kabul on Monday, killing at least six people near a police checkpoint, including policemen, officials said, but no militant group has yet claimed responsibility.
Six people were killed in the explosion, said Najib Danish, a spokesman for the interior ministry. Ten policemen and civilians, including women, were injured in the blast.
The attacker on foot detonated his suicide vest close to the checkpoint near a school in central Kabul, which is in the same area as the finance and justice ministries and close to the presidential palace.
Police spokesman Basir Mujahid said he was about 20 metres (66 ft) away from the blast, near where a demonstration had broken up some 30 minutes before.
"I took four bodies away but there were more on the ground," he said, without giving further details.
TRT World's Sultan Faizy has more details from Kabul.
Hundreds of protesters, including university students, had taken to the streets of Kabul to demand the deployment of reinforcements to Hazara-dominated districts in Ghazni province which have been attacked by the Taliban.
The explosion came as Afghan security forces have been suffering scores of casualties in heavy fighting with Taliban militants in two provinces.
Heavy fighting in Ghazni
Dozens of elite commandos were among the casualties suffered by Afghan security forces as the Taliban claimed to have taken a district in Ghazni province, stepping up battlefield pressure while seeking a political settlement with the United States.
Officials said about 25 Afghan commandos were killed in central Ghazni, where the Taliban have been battling militia from the mainly Shia Hazara community in the districts of Malistan and Jaghori, a conflict coloured by hostility between ethnic Hazaras and Pashtuns.
US forces were providing assistance, including intelligence and close air support, a spokeswoman from US military headquarters in Kabul said.
Taliban spokesman Zabiullah Mujahid said Malistan had fallen but local security officials said fighting continued close to the district centre.
“Fresh troops have been sent to Malistan and Jaghori but the people are also cooperating and have stood up against the insurgents,” Army General Chief of Staff, Mohammad Sharif Yaftali, told reporters.
Some commandos had been killed or wounded, he added, but gave no details.
However security officials, speaking on condition of anonymity, said the commandos had been rushed in to unfamiliar territory and ambushed by Taliban fighters, many of whom now regularly use night vision equipment.
Afghanistan’s highly regarded special forces units have suffered increasingly heavy casualties this year as the Taliban have mounted major assaults on provincial centres including Ghazni city and Farah city in the southwest.
At the same time as the Ghazni fighting on Sunday, about 50 police and soldiers were killed around Farah when Taliban fighters attacked check posts in the city and nearby districts, regional officials said.
US commanders have said they expect the Taliban to step up military efforts to better their position while they maintain contacts with US special envoy Zalmay Khalilzad aimed at opening peace negotiations.
Khalilzad, an Afghan-born former US ambassador to Kabul, met President Ashraf Ghani and other officials at the weekend, in his latest round of meetings following an initial meeting last month with Taliban officials in Qatar.
But Sunday’s fighting underscores the pressure on Afghanistan’s overstretched security forces, suffering from their highest level of casualties ever, estimates from the NATO-led Resolute Support mission show.
The government no longer releases exact casualty figures but officials say at least 500 men are being killed each month and hundreds more wounded, a tally many consider an underestimate.