The United States warned Saudi Arabia, which has a Sunni Muslim majority, that its execution Saturday of a prominent Shia cleric behind anti-government protests "risks exacerbating sectarian tensions."
The US also urged Riyadh to "respect and protect" human rights, said State Department spokesman John Kirby, following the execution of Nimr al-Nimr.
Another 46 men were executed, including Shia activists and Sunnis accused of involvement in Al-Qaeda killings.
The executions sparked angry condemnation from Shia-majority Iran and Iraq, while the EU similarly expressed concern about possible "dangerous consequences" in a region already fraught with sectarian tensions.
Some of the executed were beheaded, while others were shot by firing squad.
"The United States also urges the government of Saudi Arabia to permit peaceful expression of dissent and to work together with all community leaders to defuse tensions in the wake of these executions," Kirby said in a statement.
"We are particularly concerned that the execution of prominent Shia cleric and political activist Nimr al-Nimr risks exacerbating sectarian tensions at a time when they urgently need to be reduced.
"In this context, we reiterate the need for leaders throughout the region to redouble efforts aimed at de-escalating regional tensions."