"extended congratulations" is correct and can be used in written English.
It is used to give a longer lasting congratulations than a simple "congratulations". Example sentence: I want to extend my congratulations to my friend for successfully completing their doctorate degree.
He extended congratulations on the recent U.S. elections.
Stop Kony!!! RT @KendallJenner: please WATCH THIS… vimeo.com/37119711 — Kim Kardashian (@KimKardashian) March 7 , 2012And the White House press secretary, Jay Carney, said President Obama extended congratulations to the people who mobilized to promote a viral Web video about the atrocities carried out by the Lord's Resistance Army.
Taylor's winning dart at double 16 sparked an altercation between the two players, when after an initial handshake, the man from Stoke-on-Trent refused Van Barneveld's extended congratulations.
I am honored!!" Many other Trump-supporting Reddit users extended congratulations, with one admirer calling HanAssholeSolo a "legend".
Governor General Michaëlle Jean and Prime Minister Stephen Harper of Canada extended congratulations on behalf of Canadians, while Mexican President Felipe Calderón wished Obama "great success in the work as the new President of the United States".
There are several good reasons why president Barack Obama should join his White House guest this week, Egypt's president Hosni Mubarak, as well as the UN's Secretary General, Ban Ki-Moon, and dozens of other world leaders who have extended congratulations to Iran's duly re-elected president, Mahmoud Ahmadinejad.
I begin by extending congratulations on his victory.
I'd like to take the opportunity to extend congratulations to these individuals.
A statement on http://www.avfc.co.uk read: "Villa would like to extend congratulations to the Duke and Duchess of Cambridge on the arrival of their baby boy.
MONDAY'S PUZZLE — Before we get started with our solving week, Wordplay would like to extend congratulations to John Hammond, winner of the 2012 Brown University Crossword Tournament.
A number of world leaders, including President Clinton, President Jiang Zemin of China and Prime Minister Tony Blair of Britain, spoke with Mr. Putin by telephone today, extending congratulations and expressing their own hopes for Russia's future.
