WASHINGTON - The Latest on a Senate committee's hearing into the president's authority to launch nuclear weapons (all times local):

11:17 a.m.

A former senior U.S. military officer says an order from the president to launch nuclear weapons can be refused if that command is determined to be illegal.

Retired Air Force Gen. Robert Kehler told the Senate Foreign Relations Committee on Tuesday the U.S. armed forces are obligated to follow legal orders, not illegal ones.

Kehler served as commander of Strategic Command from January 2011 to November 2013.

He says the legal principles of military necessity, distinction, and proportionality also apply to decisions about the use of nuclear weapons.

Sen. Ben Cardin of Maryland asked Kehler if that means the top officer at Strategic Command can deny the president's order if it fails those tests.

Kehler says, "Yes." But he says that would lead to a "very difficult conversation

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10:30 a.m.

Sen. Bob Corker, the Foreign Relations Committee chairman, says the panel's hearing on the president's authority to use nuclear weapons isn't a rebuke of President Donald Trump.

This is the first time in 41 years the committee is looking specifically at nuclear weapons use.

Trump over the weekend exchanged school-yard taunts with North Korea's Kim Jong Un. The provocative remarks and others by Trump aimed at Pyongyang have sparked concerns among lawmakers that he may be inciting a war with North Korea.

But Corker, a Tennessee Republican, says the session is one of a series to examine war making, the use of nuclear weapons, and conducting foreign policy overall.

He says, "This is not specific to anybody."

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3:37 a.m.

The Senate Foreign Relations Committee is looking into the president's unchecked authority to use nuclear weapons.

The committee led by Republican Sen. Bob Corker of Tennessee plans to hear testimony from a former commander of the Pentagon's nuclear war fighting command and other witnesses.

Corker says numerous lawmakers have raised questions about legislative and presidential war-making authorities and the use of America's nuclear arsenal. He calls a discussion on the topic "long overdue."

The question of whether anyone could stop a president from ordering a pre-emptive nuclear strike was rarely raised before Donald Trump ran for the White House.

The answer to the question is simple: No. Under the long-established protocols, neither the Congress nor the defence secretary can stop the president. Military officers are duty-bound to execute the order.

News from © The Associated Press, 2017