MILAN, Jan 24 (Reuters) - Italy will take legal action and step up pressure in Brussels against Pfizer Inc and AstraZeneca over delays in deliveries of COVID-19 vaccines with a view to securing agreed supplies, Foreign Minister Luigi Di Maio said on Sunday.

The aim was to get the companies to meet the vaccine volumes they had promised and not to seek compensation, Di Maio said on RAI state television.

"This is a European contract that Pfizer and AstraZeneca are not respecting and so for this reason we will take legal action... We are working so our vaccine plan programme does not change," he said.

Pfizer said last week it was temporarily slowing supplies to Europe to make manufacturing changes that would boost output. On Friday, AstraZeneca said initial deliveries to the region will fall short because of a production problem.

Asked why he thought the pharmaceutical companies had been forced to announce reductions, Di Maio said he believed they had simply bitten off more than they could chew.

"We are activating all channels so the EU Commission does all it can to make these gentlemen respect their contracts," he said.

No one was immediately available to comment at Pfizer in Italy. AstraZeneca did not immediately reply to an email and voice message.

Also on Sunday European Council President Charles Michel said the EU would use legal means to ensure pharmaceutical companies respect supply contracts for COVID-19 vaccines.

"We plan to make the pharmaceutical companies respect the contracts they have signed ... by using the legal means at our disposal," Michel said on Europe 1 radio.

Sky Italia TV cited Pfizer on Sunday as saying the cuts, to the number of vials delivered and not the number of doses, had been due to work to increase capacity at a Belgian plant.

Supplies would return to normal as of next week, Sky cited Pfizer as saying.

On Saturday Italian Prime Minister Giuseppe Conte said the delays in vaccine supplies were "unacceptable" and amounted to a serious breach of contractual obligations, adding that Italy would use all available legal tools.

Speaking on Italian TV on Sunday Italy's Deputy Health Minister Pierpaolo Sileri said the cut in supplies announced by Pfizer and AstraZeneca would put back vaccination of the over-80s in Italy by about four weeks and the rest of the population by about 6-8 weeks.

"This kind of delay affects the whole of Europe and a good part of the world but I am confident the delay can be made up for further down the road," he said.

Italy was the first Western country to be hit by the virus last March and has registered 85,461 deaths so far, the second-highest toll in Europe after Britain and the sixth-highest in the world. (Reporting by Stephen Jewkes; Editing by Edmund Blair and Philippa Fletcher)