The Pompey winger's part of Stephen Kenny's 27-man set-up ahead of friendlies with Andorra and Hungary next month.
It represents more international recognition for Curtis, who scored 14 goals in 50 games for the Blues this season.
The former Derry man has won six caps for Eire since making his maiden senior bow in 2018.
Curtis is hoping to secure a move away from Pompey this summer as he bids to step up to the Championship.
Cardiff are reportedly one club who hold strong interest, with manager Mick McCarthy workining with Curtis when in charge of the Republic.
Blackburn, Reading and Brentford have all been linked in the past.