Kabul, Afghanistan (CNN) As Afghanistan mourned another deadly attack Sunday -- one that raises questions about the potential for stability in the region -- a top American general says US victory in Afghanistan is still a possibility.

The Afghan government declared a national day of mourning after an ambulance packed with explosives blew up in a crowded street in the capital of Kabul, killing 103 people.

The Taliban claimed responsibility for the Saturday attack, which injured 235 people, including 30 police officers, Kabul police chief Basir Mojahid said. It comes a week after militants stormed a Kabul hotel and killed scores in a 12-hour standoff.

Flags were flown at half-staff nationwide after the latest attack. The government set aside Monday as a public holiday and Tuesday as a day of prayer for the victims, according to presidential spokesman Shah Hussain Murtazawi.

The blast Saturday occurred after the ambulance passed through a security checkpoint, Interior Ministry spokesman Nasrat Rahimi said.

Police identified the attacker at a second checkpoint, Rahimi said, but couldn't stop him before he detonated the explosives in a central area near the old Interior Ministry building, a hospital and diplomatic buildings.

The attack, in the heart of what's considered the most secure part of the city, renewed doubts over Afghan authorities' ability to keep people safe.

Meanwhile, the head of US Central Command, Gen. Joseph Votel, told CNN that the attacks do nothing to dampen the United States' resolve to help Afghanistan, and that victory in the war-torn country remains "absolutely, absolutely" possible.

Hotel siege

Afghanistan has had a deadly few days, with ISIS attacking an office of the aid group Save the Children in the eastern city of Jalalabad on Wednesday, killing at least four people and injuring dozens.

Last weekend, gunmen attacked the Intercontinental Hotel in Kabul, killing at least 22 people during a 12-hour standoff with Afghan security forces. Six gunmen were killed. The Taliban also claimed responsibility for that assault.

Saturday's bombing was not just another attack in the Afghan capital. Every time the so-called "ring of steel" in the city is penetrated, it challenges the government's ability to remain in control of even its most important sanctuaries.

Strategy change for Taliban?

The Taliban's swift claim of responsibility marked a contrast to a March attack on a key military hospital in Kabul that killed at least 30 people, many of them doctors and injured soldiers. The Taliban denied it was behind the hospital attack, and ISIS eventually claimed it.

This time, the Taliban had no such qualms. It's possibly a sign the Taliban doesn't want to lose out to its younger, nastier rival insurgency in the extremism stakes. A year ago, medical facilities were off-limits; now, an ambulance can be used as a bomb.

US President Donald Trump condemned the attack.

"This murderous attack renews our resolve and that (of) our Afghan partners," Trump said in a statement.

"The Taliban's cruelty will not prevail. The United States is committed to a secure Afghanistan that is free from terrorists who would target Americans, our allies, and anyone who does not share their wicked ideology. Now, all countries should take decisive action against the Taliban and the terrorist infrastructure that supports them."

The head of the UN mission in Afghanistan said the attack was "nothing short of an atrocity" that targeted a civilian area.

"While the Taliban claim suggested the purpose of the attack was to target police, a massive vehicle bomb in a densely populated area could not reasonably be expected to leave civilians unharmed," Tadamichi Yamamoto said in a statement.

Strongholds vulnerable?

The latest attack comes at a crucial moment in the 16-year Afghanistan war. Last year, US and Afghan officials accepted that things had not gone well -- that territory had been lost. This year, they insist, the Taliban will begin to lose territory again. Attacks such as this not only diminish morale but show strongholds as vulnerable.

A wounded woman is assisted at the site of the attack Saturday in Kabul.

Hundreds more US troops are en route to Afghanistan to begin a much riskier mission: training Afghan troops outside the wire. The mission will put Americans on the front lines, possible in deadly combat situations.

Speaking at an airbase outside Amman, Jordan, on Sunday, Gen. Votel said the recent attacks have served only to bolster the US commitment to Afghanistan.

"(The attacks do) not impact our commitment to Afghanistan, our commitment to the mission and seeing this through and our commitment about making sure that the Afghan national security forces have what they need to deal with this particular enemy," he told CNN. "As horrible as this is, to me, it strengthens our resolve to help them move forward."

Votel was in Jordan for a ceremony celebrating the delivery of Black Hawk helicopters to the nation. There, he also emphasized US commitment to its Arab ally, which borders Israel, Syria and Iraq.

"Jordan has been a fantastic partner for a number of years," the general said. "I think what you saw in our demonstration here today is the maturity of our relationship. Jordanians are operating top-of-the-line equipment and doing a great job with it."

Votel was also pressed on an issue closer to Jordan -- a Turkish demand that the US withdraw its troops from Manbij, in northern Syria's Aleppo Governorate, so as to allow Turkish forces to take on US-backed Kurdish forces in the region. He said such a withdrawal wasn't in the offing.

"Right now, it's not something we're looking into," he said.