The statistics bureau said construction remained robust despite slowing a notch from the previous month, as infrastructure investment speeded up, boosting demand for steel.
Ireland's manufacturing sector posted its fastest growth in nearly two years in May, according to a survey published on Thursday.
Employment growth rose to its fastest pace in two years with a number of respondents saying they had taken on new staff on expectations of further workload increases.
The May result was slightly lower than a preliminary reading of 54.0 but remained comfortably above the 50-point line dividing expansions in activity from contractions. "Last month we outlined our belief that the outlook for Irish manufacturing firms remains positive, supported by the improving worldwide backdrop", Mr O'Sullivan said.
Survey respondents reported that the weak exchange rate had led to intense negotiations with suppliers, but some noted that the peak phase of price hikes for imported materials had now passed.
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The official non-manufacturing PMI, a gauge for the service sector, rose to 54.5 percent from 54 percent in April.
Markit said weaker new business growth and softer job creation helped to offset a marginally stronger upturn in production volumes. He added that panellists reported weak demand both domestically and overseas, citing disappointing sales in nearby Asian economies.
Separately, South Korea's central bank survey on local manufacturers also showed more optimism for future business conditions, with the June business survey index rising to more than three-year high.
Because output fell for the first time in four months in May, the report said the rate of contraction was faster than the series average. With regards to future performance, goods producers were the most optimistic in last next six months, with firms expecting new product launches, machinery acquisitions and marketing campaigns to support output growth in the year ahead.
Strong competitive pressures forced manufacturers to lower their factory gate prices as cost burdens grew, squeezing profit margins.
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Ukip member Abigail Eatock won loud applause as she told the PM: "You said you wouldn't call an election and you did". May had said she was too busy "thinking about Brexit negotiations" and "meeting voters" to take part in the debate.