A spokesman for President Hamid Karzai said U.S. military prosecutors should appeal the cases and push for harsher penalties.
One soldier has been sentenced to two months in prison, another to three months. A third was demoted and given a letter of reprimand and a fine. A fourth was given a reduction in rank and pay.
"The punishments given to those soldiers were very light and unexpectedly lenient," said presidential spokesman Karim Rahimi. "This is a very serious issue. They should receive severe punishments."
He said the government was considering bringing the matter up with U.S. authorities.
A member of the Afghan Independent Human Rights Commission was even harsher in his criticism.
"These punishments are a joke. They all should have got 20 years in prison or be sentenced to death," said Ahmad Shah Midad. "A person's life has been taken. They must be punished properly."
The courts-martial had occurred in the U.S. state of Texas over the past few weeks. The soldiers were charged in relation to the deaths of two Afghans who were in detention at Bagram, the main U.S. base in Afghanistan, in late 2002.
One of the two was a 22-year-old taxi driver known only as Dilawar. The other was Mullah Habibullah, who was about 30.