'Most reckless president'

Fifty senior Republican national security officials have issued a stinging rejection of their party's White House nominee Donald Trump, warning if elected he would be "the most reckless president in American history".

The group, some of whom had already announced they would not vote for Trump, included former homeland security chiefs, intelligence directors, senior presidential advisors and a former US trade representative. They served under Republican presidents from Richard Nixon to George W. Bush.

"We are convinced that he (Trump) would be a dangerous president and would put at risk our country's national security and well-being," they wrote in a statement published in The New York Times on Monday.

Trump has raised concerns over his scant knowledge about global defense and security architecture, and his readiness to scuttle America's central role in the Nato military alliance. Further to the shock and dismay of many in America's political class, he has even questioned why the nation has bothered to develop nuclear weapons if it has no intention of putting them to use.

While the US security experts did not say they would vote for Democratic presidential nominee Hillary Clinton -- indeed they expressed "doubts" about her -- they were clear in stating that "none of us will vote for Donald Trump."

They essentially declared the brash billionaire unfit for office.

"He is unable or unwilling to separate truth from falsehood," the group wrote, saying Trump possesses a set of "dangerous qualities" that should disqualify him from the presidency. "We are convinced that in the Oval Office, he would be the most reckless president in American history."

The signatories included Tom Ridge and Michael Chertoff, the first and second homeland security secretaries under president George W. Bush, former director of National Intelligence John Negroponte and Bush-era CIA director Michael Hayden.

Trump issued a sharply worded reprimand of the group, painting them as "nothing more than the failed Washington elite looking to hold onto their power" and saying they should be "held accountable" for making the world less safe.

CLINTON SUED OVER BENGHAZI

Meanwhile, Relatives of two men killed in the 2012 attack on a US consulate in Libya have filed a lawsuit blaming the deaths on Hillary Clinton's "reckless" handling of classified information in her private email server.

Parents of two American security agents at the consulate in their wrongful death suit file Monday against Clinton allege that terrorists were able to determine the men's whereabouts because of her use of a private server.

The assault on the US consulate, which occurred while Clinton was secretary of state, killed four Americans in all, including Washington's ambassador to Libya Christopher Stevens.

The FBI concluded last month that the Democratic presidential nominee had been "extremely careless" with classified information on her server, but nevertheless declined to recommend criminal charges against her over the scandal.