ROME, Jan 25 (Reuters) - The Italian government on Monday sent a letter of formal notice to Pfizer calling on the drug company to respect its contractual commitments over its COVID-19 vaccine deliveries, the government special commissioner said.

The letter adds to tension between the European Union and the U.S. drug-maker, which announced last week a temporary slowdown in deliveries to the bloc.

"The State Attorney General's Office has sent Pfizer a formal notice to comply with its contractual obligations relating to its failure to deliver vaccine doses," the special commissioner office said in a statement.

Pfizer declined to comment beyond its previous statement. Pfizer said on Jan. 15 it will make up for the slowdown in deliveries with manufacturing changes that will boost output.

The government statement added the special commissioner will also assess in the coming hours what further action to take at national and European levels.

If Pfizer does not meet its contractual obligations, the drug group could be accused of breaching the contract it has signed with the European Union on member states' behalf, an Italian source familiar with the matter said.

The company will be given a few days to respond, at most one week, the person added.

Maker of the rival AstraZeneca vaccine also said initial supplies to the continent would fall short because of a production glitch.

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

(Reporting by Angelo Amante; Additional reporting by Michael Erman in New York and Emilio Parodi in Milan and Domenico Lusi in Rome; Writing by Giselda Vagnoni; Editing by Lisa Shumaker)