The Pentagon has officially started a review of the U.S. nuclear posture, it announced Monday.

“Today, Secretary [James] Mattis directed the commencement of the review, which will be led by the deputy secretary of defense and the vice chairman of the Joint Chiefs of Staff, and include interagency partners,” Pentagon spokeswoman Dana White said in a statement. “The process will culminate in a final report to the president by the end of the year.”

The nuclear posture review was ordered by President Trump in a January executive action on military readiness.

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The January memo called for a review “to ensure that the United States nuclear deterrent is modern, robust, flexible, resilient, ready and appropriately tailored to deter 21st-century threats and reassure our allies.”

Though planned since January, the start of the nuclear review comes at a time of high anxiety over increasing tensions on the Korean peninsula.

The last time the military conducted a nuclear posture review was in 2010.

Earlier this month, Gen. John Hyten, commander of U.S. Strategic Command, told the Senate Armed Services Committee that the new review had “just kicked off.”

Lt. Cmdr. Courtney Hillson, a Pentagon spokeswoman, told The Hill on Monday that Hyten was referring to "preliminary work."

Rep. Adam Smith David (Adam) Adam SmithWhen 'Buy American' and common sense collide Overnight Defense: Marine Corps brushes off criticism of Marines' appearance in GOP convention video | US troops injured in collision with Russian vehicle in Syria | Dems ask for probe of Vindman retaliation allegations Democrats press Pentagon watchdog to probe allegations of retaliation against Vindman brothers MORE (D-Wash.), ranking member of the House Armed Services Committee who has been critical of costly nuclear modernization efforts, said Monday he hopes the review includes a "thoughtful assessment" to "rethink what the priorities should be for a strong yet affordable nuclear arsenal."

“In the past, nuclear posture reviews have considered in depth the crucial role played by efforts to enhance strategic stability and prevent nuclear proliferation," he said in a statement. "It is important that this review do the same. I hope that it includes a thorough assessment of policy options that would allow us to avoid a costly and dangerous nuclear arms race; and that it properly analyzes the enormous risks inherent in lowering the threshold for using nuclear weapons."

Hyten told the Senate committee the review will start by looking at threats from countries such as Russia, China, North Korea and Iran. It will also look at the modernization plans for the nuclear triad, a three-pronged nuclear defense arsenal, he said.

Hyten and Gen. Paul Selva, vice chairman of the Joint Chiefs of Staff, have also said the review will include options to respond to Russia’s violation of the Intermediate-Range Nuclear Forces Treaty.

In a House Armed Services Committee hearing in March, Selva said the review will look at potential strategy changes to respond to Russia’s apparent willingness to use nuclear weapons.

“We’ve begun an investigation of a series of potential strategy changes, many of which will have to be incorporated in the nuclear posture review,” he said. “In the prior administration, we looked to limit the potential use and utility of nuclear weapons in any scenario with an eye toward reducing the numbers to a much smaller inventory than we have today, a noble goal to be sure.

“One of the things that happened in the context of that conversation is our adversaries started to articulate a doctrine of escalation to deescalate, and we have to account for in our nuclear doctrine what that means and what the ladder of strategy ability implies as we look at an adversary that expresses in their rhetoric a willingness to use nuclear weapons.”

Ellen Mitchell contributed.

Updated at 4:43 p.m.