A poignant letter written by former U.S. President Abraham Lincoln to a group of schoolchildren sold for $3.4 million US at a Sotheby's auction in New York Thursday.

The auction house said the final bid broke previous records for presidential manuscripts.

Lincoln wrote the letter in 1864 in response to a petition signed by 195 Massachusetts children asking him to "free all the little slave children."

Lincoln's letter reads:

"Please tell these little people I am very glad their young hearts are so full of just and generous sympathy, and that, while I have not that power to grant all they ask, I trust that they will remember that God has, and that, as it seems, He will to do it."

An American collector won the auction, bidding over the phone.

A Lincoln manuscript outlining his postwar reconstruction plan broke records in 2002, fetching $3.1 million US at a Christie's auction in New York.

Other items up for sale in the Sotheby's auction include letters from other U.S. presidents such as Thomas Jefferson and Millard Fillmore. The collection was amassed by New York-based physician Robert Small.

With files from the Associated Press