Sen. Rand Paul (Manuel Balce Ceneta/AP) Sen. Rand Paul (Manuel Balce Ceneta/AP)

A top aide to Sen. Rand Paul (R-Ky.), who has been dealing with a series of plagiarism allegations in recent days, acknowledged Tuesday that Paul's staff in some cases failed to properly attribute and quote content pulled from other sources.

"In the thousands of speeches and op-eds Sen. Paul has produced, he has always presented his own ideas, opinions and conclusions," senior adviser Doug Stafford said in a statement. "Sen. Paul also relies on a large number of staff and advisers to provide supporting facts and anecdotes — some of which were not clearly sourced or vetted properly."

Stafford also pointed to failures to properly quote text from other sources that should have been clearly labeled as such.

"There have also been occasions where quotations or typesetting indentations have been left out through errors in our approval process," Stafford said. "From here forward, quoting, footnoting and citing will be more complete."

Stafford said footnotes will be available "on request."

"Adherence to a new approval process implemented by Sen. Paul will ensure proper citation and accountability in all collaborative works going forward," he said.

Paul in recent days has been shown to have borrowed phrasing from Wikipedia, the conservative Heritage Foundation, the libertarian Cato Institute and other sources in his speeches and his recently released book. In the latter case, Paul's book cribbed more than 1,000 words of a Heritage study.

MSNBC first reported on the plagiarism allegations last week, followed by BuzzFeed and Politico.

He previously said the plagiarism allegations were the result of "haters" and suggested that he properly cited the material, while also acknowledging that more could have been done.

He defended himself as late as Monday night, saying he has made mistakes but that he has always "tried" to do things properly.

"We have tried at every possible point to attribute things," he said on Fox News's "Hannity." "And nothing was ever intentionally used.  We give credit to Heritage I think 15 times in the book, to Cato 12 times. And do we always do it properly? Maybe not, but we tried."

Paul is considered a leading GOP presidential candidate in 2016.

Update 1:07 p.m.: The New York Times reports on another example of Paul using the same language as someone else, from an op-ed he wrote for the Washington Times.