The US embassy in Riyadh has warned its citizens against travelling to the Shiite village of Awamiya in eastern Saudi Arabia, where gunmen this week attacked the car of two German diplomats.
Berlin has said it has no reason to believe the Monday attack in Awamiya, in the Shiite-populated Eastern Province, was politically motivated.
The US embassy said in a statement on its website it had "re-instructed its employees and their family members to avoid Awamiya and advises all US citizens to do the same".
"Regardless of where you are, it is always advisable to keep your security and situational awareness levels high," the statement said, while urging Americans to "avoid crowds or large gatherings when travelling in public".
The Germans' car was hit by bullets but they escaped unharmed.
German foreign ministry spokesman Martin Schaefer said Wednesday the area was known for "security risks".
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"We have no evidence and no concrete indications that this attack on the two German diplomats had a terrorist motive, a political motive," he told reporters in Berlin.
The official SPA news agency said Saudi authorities are hunting for the gunmen, without saying whether the incident was linked to unrest in Eastern Province.
Protests first erupted in the province, home to the majority of the kingdom's two million Shiites, in March 2011.
Since then 10 people have been killed in clashes with security forces.
Fighting intensified after the arrest in July 2012 of Sheikh Nimr al-Nimr, considered to be a driving force behind the protests.
However, tensions eased in August that year when seven Shiite dignitaries from Qatif, where Awamiya is located, hailed a call by King Abdullah for the creation of a centre for Sunni-Shiite interfaith dialogue.