Apple/Mac Dictionary: procurements: the action of obtaining or procuring something : financial assistance for the procurement of legal advice | the company's procurements from foreign firms.
• the action or occupation of acquiring military equipment and supplies : defense procurement.

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Note added at 15 mins (2014-11-13 11:25:44 GMT)
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All results for the search word 'procurements', here as well: http://www.oxforddictionaries.com/definition/english/procure...

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Note added at 16 mins (2014-11-13 11:27:34 GMT)
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Besides, 'public procurement' is a special way of getting suppliers, most often for projects for the public good and making the request public, so this word can't be substituted by 'purchases' or anything else.

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Note added at 2 hrs (2014-11-13 13:51:52 GMT)
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As far as I know, "comply with one or more public procurement rules", "the public procurement procedure launched pursuant to Council Decision..., "values referred to in the public procurement directives may be awarded...", "pursuant to a public procurement procedure","service for which public procurement has been announced", "simplify public procurement procedures" can be found on Wordbee and in actual papers, but it's very rare that you collocate a verb with it. My guess would be that one 'can follow a p.pr. procedure', 'act on a p.pr.', perhaps even 'execute a p.pr.', but I don't remember ever seeing such phrases.

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Note added at 2 hrs (2014-11-13 13:56:31 GMT)
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Furthermore, I'd find it strange that, as you've asked, an agency may be 'responsible for ogranising and performing public procurement(s)'. It's not the plural, but the fact that p.pr's are usually made public by governmental bodies, so I'd find your sentence strange from this point of view.

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Note added at 8 hrs (2014-11-13 19:36:12 GMT)
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Asker, in that case, it's a possible sentence, although in Hungary, for example, I don't think we would call those bodies agencies, rather government offices, but agency could also be an option. In Eastern Europe, a lot of things may happen, so go along with that if you know. All in all, the plural is not often used, but can be used, also in your sentence.