Rahman Shah was standing in line at a security checkpoint with his wife and three children early Saturday when he heard someone shout "suicide attack." He turned to see a police officer chasing a man, and moments later a blinding explosion threw him and his family to the ground.

"I fell to one side of the road with my son, and when I ran to the other side where my wife, daughter and my other son were, I found them all injured and bloody," Shah said from the side of a hospital bed where his wife and 4-year-old daughter were recovering.

Twelve people were killed and at least 42 injured when the bomber blew himself up in a busy pedestrian alley next to Afghanistan's Interior Ministry, officials said. The blast was the second major suicide attack in Kabul this month, underscoring the rising danger in the once-calm capital as militants step up attacks across the country.

Interior Ministry spokesman Zemeri Bashary said 12 people were killed, including two women and a child, and that 42 were wounded. Dr. Salam Jalali, a Public Health Ministry official, said 54 had been wounded.

The explosion occurred just before 8 a.m. on an Afghan work day, near a narrow dirt road where employees and civilians pass through a security gate. Shops, street photographers, and men who fill out Interior Ministry paperwork for illiterate Afghans make the area a busy cross-section of commerce and government.

President Hamid Karzai condemned the blast and said that "suicide attackers come from outside Afghanistan and target the most devoted and the poorest Muslim people of the world."

"I condemn it in the strongest terms and call on the international community to work with Afghanistan in stopping sanctuaries that raise, train and brainwash young people to become suicide attackers," Karzai said in a statement.

Bashary said the suicide attacker had been acting suspiciously, then tried to get close to a gathering of people just beyond a police checkpoint.

A witness said he saw the bomber run from police, who had tried to search him.

"The bomber ran into the area (past the checkpoint), and the policeman took out his gun — this all happened very fast — and then the guy detonated himself," said Ahmed Ramin, 18.

Militants have been stepping up attacks including roadside and suicide bombings across Afghanistan during the last several months.

Earlier this month a suicide car bomber rammed a U.S. military convoy in Kabul, killing 16 people, including two American soldiers, and a suicide bomber killed 18 people in an attack outside the Helmand provincial governor's compound in the town of Lashkar Gah on Tuesday.

Maj. Luke Knittig, a spokesman for NATO's international security force that controls much of Afghanistan, said Saturday's attack shows that the insurgents "recognize the significance of this nation's capital."

"They recognize we have them under pressure in their strongholds in the south and the east, so this does fit into, sadly, what we expected somewhat to see, them resorting to this kind of tactic, hitting softer targets and getting the additional significance attached to hitting the nation's capital," he said.

Knittig said there is a recognition of a rising threat in the capital, and that citizens need to be more vigilant.

"But look at all the commerce and activities (in Kabul)," Knittig said. "There's a little bit of why the insurgents try to carry out attacks in the capital."

In other violence, four police were wounded Saturday when their vehicle was hit by a roadside bomb in the southern province of Kandahar, said police official Raz Mohammed. The four were traveling on the main highway connecting Kandahar with the western province of Herat.