Republican presidential nominee Donald Trump declared a $916m loss on his 1995 income tax returns and the large tax deduction may have allowed him to avoid paying federal income taxes for up to 18 years, according to report in the New York Times.

In a statement responding to the Times report, the Trump campaign said that the tax document was obtained illegally and that the New York Times is operating as an extension of the presidential campaign of Democratic rival Hillary Clinton.

The Times said it had obtained Mr Trump's 1995 tax records and that they showed he received the large tax benefits from financial deals that went bad in the early 1990s.

The newspaper said that tax experts it hired to analyse Mr Trump's records said tax rules which are especially advantageous to wealthy filers would have let Mr Trump use his $916m loss to cancel out an equivalent amount of taxable income over an 18-year period.

The Times said that although Mr Trump's taxable income in subsequent years is as yet unknown, a $916m loss in 1995 would have been large enough to wipe out more than $50m a year in taxable income over 18 years.

Mr Trump has declined to release his tax records, unlike previous presidential nominees in modern history, saying his taxes are under a federal audit.

Experts said he could still release them publicly if he wished.

"Mr Trump is a highly skilled businessman who has a fiduciary responsibility to his business, his family and his employees to pay no more tax than legally required," the Trump campaign statement said.

"That being said, Mr Trump has paid hundreds of millions of dollars in property taxes, sales and excise taxes, real estate taxes, city taxes, state taxes, employee taxes and federal taxes, along with very substantial charitable contributions," it said.

Meanwhile, Mr Trump closed out what has been a rough week for his campaign by escalating personal attacks on Mrs Clinton.

Mr Trump questioned the stamina of Mrs Clinton, who suffered a bout of pneumonia last month, and said she should be in prison for her handling of classified emails.