At least 12 Americans were killed in Kabul on Saturday when a Taliban suicide bomber unleashed the deadliest attack on U.S. armed forces since the shooting down of a helicopter in August that killed 30 Americans.

More American blood sacrifice in a thankless beneficiary country.

It also raises doubts about the viability of the U.S. strategy of spending billions to clear Afghanistan of Taliban insurgents and prop up Hamid Karzai's corruption-ridden government.

Saturday's attack, which ranks as the deadliest single ground attack on U.S. personnel in the Afghan capital, comes a week after Kabul disowned the U.S. in the bitterest of ways. Karzai, president of Afghanistan, said last week his country would support Pakistan in the event of a U.S. attack on that country. He told a Pakistani television channel, quite unequivocally, that if the U.S. did attack Pakistan, his country would support its brother.

If fighting starts between Pakistan and the U.S., we are beside Pakistan, said Karzai, rubbing salt in to the U.S. wounds, If Pakistan is attacked and the people of Pakistan need Afghanistan's help, Afghanistan will be there with you, said Karzai, in the backdrop of worsening relationships between the U.S. and Pakistan.

Anybody that attacks Pakistan, Afghanistan will stand with Pakistan ... Afghanistan will never betray its brother, said Karzai, who was handpicked by the U.S. following the NATO-led post-9/11 invasion of the country and removal of the Taliban regime.

This is how Karzai decides to reward the United States for sacrificing more than 1,700 troops in the last decade and spending $500 billion on the conflict.

The U.S. ends up spending more money and resources, and sacrifices more lives, as Taliban rumps get support from across the borders. The U.S. believes it cannot abandon its mission in Afghanistan before it roots out the Taliban, as such a move will worsen the situation. Karzai knows this truth, but his allegiance is dictated by other principles. The truth is that Pakistan continues to harbor terrorist groups that foment trouble in Afghanistan. Splinter terror groups within Afghanistan get arms, ammunition, and financial assistance from across the borders.

Karzai issued a statement condemning Saturday's attack, but he deliberately avoided mentioning the death of a dozen Americans and offered no regrets about the loss of American lives.

The enemies of Afghanistan carried out a dastardly and cowardly attack that caused sorrow for some Afghan families, he said. The point is that most of the world knows that those enemies are drawing support from within Pakistan; the brotherly country Karzai claims he will defend, no matter what it takes.

The relationship between the U.S. and Pakistan touched a raw nerve when Pakistan clearly failed to contain the support terrorists gain from that country. However, Karzai is defiant in the face of stark reality. For him, a tribal show of solidarity is more valuable than the enormous cost and sacrifice the U.S. has suffered to keep his country safe from debilitating insurgency.

Does he forget that without U.S. intervention Afghanistan would have remained a godforsaken country in the tight grip of one of the most oppressive regimes in the world?

Ever since American soldiers set foot on Afghan soil in the aftermath of the 9/11 attacks, the U.S. wars on terror, mostly in Iraq and Afghanistan, have cost the country a staggering $1.27 trillion, according to the Cost of War Web site. Before the U.S. is finally done with its global war on terror, the cost could jump much higher. This is way above the $1 trillion war bill projected by President Obama.

With the Taliban claiming responsibility for Saturday's attack, the terror organization has proved it still retains a considerable strike force in Afghanistan.

How will the U.S. react to this? The tragedy is that despite knowing that it is serving a thankless regime, the U.S. cannot leave treacherous Afghan terrain easily. The bold attack in Kabul by the Taliban has made it clear that the U.S. will remain enmeshed in the bloody struggle beyond the 2014 deadline for pulling out all troops.

Expect Karzai to occasionally add insult to injury.