An unknown number of one dollar George Washington Presidential coins were minted without edge lettering and went past the inspectors into circulation.

The coins have likeness of Washington with words 'In God We Trust' and 'E Pluribus Unum' along the edge as well as mint mark and year of coinage.

Admitting the lapse, the US Mint said it had struck more than 300 million such coins and an unspecified quantity of these coins inadvertently left the Mint in Philadelphia without edge lettering on them.

In a statement, it said, it takes the matter seriously and is looking into the matter to determine a possible cause in the manufacturing process.

The United States Mint understands the importance of the inscriptions 'In God We Trust' and 'E Pluribus Unum', as well as the mint mark and year on US coinage it said, adding, "we also consider quality control a high priority".

Production of the presidential one dollar, with its unique edge-lettering, is a new, complex, high volume manufacturing system, and the United States Mint is determined to make technical adjustments to perfect the process.

"As we adjust this new process, we intend to eliminate any such defects," it added.