KABUL, Afghanistan - Insurgents took aim Sunday at the Afghan security forces, ambushing an army bus in the capital, Kabul, and storming an army recruitment center in the north of the country.

The attacks came as Vice President Biden predicted that U.S. forces would leave the fighting to Afghans and be "totally out of there, come hell or high water, by 2014."

A total of at least 13 soldiers and police were killed in the two attacks, each carried out by squads of suicide bombers and gunmen.

The Afghan police and army are key factors in the West's exit strategy, which calls for Afghan forces to take over security responsibilities across the country in the next three years. That plan was endorsed at a NATO conference last month and again last week in a White House assessment of the long-running Afghan conflict.

The Taliban claimed responsibility for the two assaults, and warned that it would continue targeting Afghan forces and Western troops.

Biden said in an interview on NBC's Meet the Press broadcast Sunday that the start of a phased withdrawal next summer would be more than a token reduction.

His prediction appeared to go further than statements by President Obama, who said last month that there would be a reduced U.S. footprint in Afghanistan by 2014 but that the number of troops who would remain was still in question.

Obama has discussed maintaining a counterterrorism capability in Afghanistan after 2014. As recently as Thursday, he said the United States and its NATO allies would have an enduring presence there after 2014, although the details of that were unclear.

The Obama administration has said repeatedly that July will mark the beginning of troop withdrawals and that their size will depend on military conditions.

What will actually happen in 2014 will be influenced by many factors, including who wins the White House in 2012. So pledges in 2010 about withdrawal may be premature.

Al-Qaeda's strength, Biden said, "has been significantly degraded" as U.S. forces have gone after the network's leadership. But, he added, there has been less success in countering the Afghan insurgency, dealing with safe havens across the border in Pakistan, and creating a stable Afghan government.

"We're making progress on all fronts, more in some areas than in others," Biden said. "Are we making sufficient progress fast enough? The answer remains to be seen."

This year has been the deadliest of the nine-year-old war for the NATO force, which on Sunday announced the death of another service member, whose nationality was not immediately disclosed, in an explosion in the south of Afghanistan.

The Afghan government denounced Sunday's Taliban attacks, saying in a statement that they were carried out by "enemies who do not want our security forces to be able to strengthen themselves."

The attack on the army bus in Kabul took place during the morning rush hour on a heavily traveled road, sending motorists and passersby scrambling for cover.

"Everyone was trying to hide," said Shah Mohammad, whose house's windows were blown out when one of the attackers blew himself up.

The Defense Ministry said five soldiers were killed in the strike, which was the most lethal attack in the capital in seven months and a worrying sign of insurgents' continued ability to smuggle weapons and fighters into Kabul despite heightened security in and around the city.

The army recruiting center that was targeted in the other attack is in Kunduz, a once-peaceful northern city where insurgent activity has sharply intensified in the last year.

That attack, which also began in the early morning, set off a battle that continued for hours, heavily damaging homes and other buildings.

Four soldiers and four police officers were killed, according to Mahboobullah Saeedi, a spokesman for the Kunduz governor's office, and more than a dozen people, including civilians, were injured.

This article includes information from the Associated Press.