RIYADH

 The U.S. administration has warned its citizens in Saudi Arabia to remain cautious due to increasing security concerns in the kingdom, the second warning of its kind in 24 hours.

In response, the U.S. diplomatic mission to Saudi Arabia has suspended its consular services for Sunday and Monday.

"Due to heightened security concerns at U.S. diplomatic facilities in Saudi Arabia, the U.S. Embassy and Consulates have cancelled all consular services in Riyadh, Jeddah and Dhahran for Sunday, March 15, and Monday, March 16, 2015," the embassy said on its website.

"All U.S. citizens are encouraged to be aware of their surroundings, and take extra precautions when travelling throughout the country. The Department of State urges U.S. citizens to carefully consider the risks of traveling to Saudi Arabia and limit non-essential travel within the country," it added.

The embassy also urged U.S. citizens to "avoid crowds or large gatherings when traveling in public" and to minimize their profile while in public.

The warning came less than a day after the mission warned its citizens residing in the kingdom of what it described as extremists who plan to carry out "operations" in March that target westerners working in the petroleum industry.

The oil-rich, eastern region of Saudi Arabia is considered the center for the kingdom's Shiite population, who make up nearly 10% of the country's population of 20 million, according to unofficial Saudi figures.

Last October, unknown assailants targeted two American expatriates in capital Riyadh, killing one and wounding the other.

Saudi authorities stated at the time of the incident that the assailant was a former colleague of the victims who had been sacked from Saudi real estate developer Vinnell Arabia - which is in contract with Saudi's national guard ministry –  and that he has no links to extremist organizations.

Three months later, An American expatriate sustained wounds after an unknown attacker opened fire on his car in Saudi's eastern province of al-Ahsa.

It was the first attack of its kind since the ascent of Saudi King Salman bin Abdulaziz to the throne at the end of January.