BERLIN (Reuters) - Chancellor Angela Merkel will stand for a full four-year term in the September election, her spokesman said on Monday, amid German media speculation that she might step aside in 2015 midway through a third term.

"The chancellor is naturally standing for the full legislative period," her spokesman Steffen Seibert told a government news conference.

Earlier Bild newspaper published a story saying Merkel might step down in 2015 if she were to win re-election in September. The year 2015 would mark 10 years in power for Merkel and she would be 60 in 2015.

The newspaper, citing a new book by a Bild journalist, published quotes from Merkel telling sources that she considers "10 years to be the maximum time" someone should stay on as chancellor or state premier.

(Reporting By Gareth Jones, Michelle Martin and Erik Kirschbaum)