According to a spokesperson for the State Department's Bureau of Near Eastern Affairs, Rhonda Shore, the US administration would be raising the cases with the government of Washington's key Middle East ally.
The announcement on Wednesday comes three days after a Riyadh court sentenced the Saudis, accused of sedition and disobedience for seeking a constitutional monarchy, to jail terms of between six and nine years.
"The United States is troubled by this outcome," Shore said. "Jailing those who peacefully petition their leaders for political change is inconsistent with Saudi Arabia's recent steps toward reform, which we have welcomed."
"Moreover, the public trials of these defendants were not transparent, raising concerns about the rule of law in Saudi Arabia," she said.
President George Bush and his administration have embraced Saudi Arabia as a key partner in the war on terror and a major factor on oil markets, but have pressed Riyadh to accelerate the process of democratic reforms.
"We will be raising these cases further with the Saudi government," Shore said.
Activist Ali al-Dimaini was sentenced on Sunday to nine years in prison, Abd Allah al-Hamid to seven years and Matruk al-Falih to six years, according to Hamid's brother Isa.
The trio was among a dozen activists arrested in March 2004 on charges of demanding a constitutional monarchy. The others were released after pledging to no longer lobby publicly for reform.
The three jailed reformers were accused of "using Western terminology" in formulating their demands. They also allegedly questioned the king's role as head of the judiciary.