"Masters of the short form" Lorrie Moore and AL Kennedy go head to head on the shortlist for the world's richest award for a single short-story collection in what is being hailed as a stellar year for the genre.

After short-story writer Lydia Davis won the Man Booker International award last summer, Alice Munro took the Nobel and George Saunders the Folio, director of the €25,000 Frank O'Connor prize Patrick Cotter called the shortlist for this year's award "the strongest … in years". American writer Moore has been shortlisted for Bark, an exploration of the passage of time, and Kennedy for All the Rage, set on the "battlefield of the heart", according to its publisher.

Moore and Kennedy are up against two debut authors: US ex-marine Phil Klay, shortlisted for Redeployment, set in Iraq and Afghanistan, and Irish writer Colin Barrett's Young Skins, which takes place in a fictional corner of Ireland. The Frank O'Connor line-up is completed with two more American writers: Laura van den Berg, picked for her second book The Isle of Youth, a look at women stuck in lives of deception, and Ben Marcus, who makes the cut for Leaving the Sea. Reviewing Marcus's collection in the Guardian, Stuart Kelly called the author "one of the most stunningly original and profoundly unsettling writers of his generation".

Reading "untold" numbers of story collections to come up with the final six, said judge and American novelist Manuel Gonzales, he learned that "the form remains as challenging as ever … but when you put the short story in the hands of someone who understands its limits, who is willing to break through these limits, what you get is sublime, unsettling, emotionally fraught."

"What's great about the story is that for so long no one in the real world paid it much attention," Gonzales continued, "and during that time writers took liberties with the story, broke it apart, turned it over and around, tested to see what it could do, what they could do with it, and now that the short story is making a comeback – so some say – we, as readers, get to enjoy all this game play, this tinkering that's been quietly operating in the background while no one noticed it."

According to fellow judge Matthew Sweeney, Lorrie Moore and AL Kennedy could be seen as the big hitters on the 2014 shortlist, "both having long proved themselves to be masters of the short form", while Van den Berg and Marcus "have delivered extremely assured bodies of work". Klay's collection is "a brilliantly exact picture of what happens in war, and its aftermath", and Barrett "has produced a strikingly original and funny, if pungent debut work," said Sweeney.

The final judge on the panel, novelist Alison MacLeod, said the six collections were "extraordinary works" which create "entire worlds that are alive and in motion".

"The stories in these collections moved me, provoked me, and knocked the breath out of me.  They take the reader down deep; they bring him or her up short.  With every great short story – and they are numerous across these six collections – the world expands.  So does life itself.  With a powerful collection, one grows bigger by at least several lives," she said.

Won in the past by Haruki Murakami and Edna O'Brien, this year's Frank O'Connor-winning writer will be announced in early July.