Ulster Rugby have signed scrum-half Michael Heaney and back-rowers Sean Doyle and Nick Williams.

Heaney has rejoined the club from Doncaster Knights on a four-month short-term deal, with the opportunity of a full-time contract at the end of that period.

A graduate of the Phoenix Ulster Academy, Heaney has represented Ulster at all levels and made his senior debut for the province in a pre-season friendly away to Harlequins in August 2010.

He was a member of the Ireland U20 squad that won the 2010 Six Nations Championship and also competed in the IRB Junior World Championships later that year.

Doyle is an Australian-born openside flanker who has joined from Sydney club side Southern Districts.

The Irish-qualified 22-year-old has been one of the leading players in the New South Wales Premier Grade over the past four seasons and has also been a strong performer for the NSW ‘A’ representative side.

Williams, a 28-year-old New Zealander, has signed a two-year deal with the northern province.

He has previously played for the Blues and North Harbour in his homeland, before moving to Europe and spending time with Munster and Aironi.

Ulster's Director of Rugby David Humphreys claimed the arrival of Williams will add strenghten the Heineken CUp finalists' option in the pack.

“Nick was a standout player during his time at Aironi and he will add a great deal to our squad.

"His addition means there will be real depth right across the back row and this is vital, given that Stephen Ferris is under an IRFU Player Management Programme.

“(Ulster coach) Mark Anscombe brought him out of club rugby in New Zealand and believes he can make a huge impact here at Ulster. He is an excellent ball carrier and is a very physical in defence,” added Humphreys.