German construction company Hochtief admitted to breaking insider trading rules in Australia in 2014, the nation's financial regulator said on Tuesday as the firm said any breach was "inadvertent".

The Australian Securities and Investment Commission (ASIC) said it had started legal action against holding company Hochtief Aktiengesellschaft.

It said it was "seeking a declaration of contravention and a financial penalty order against the company for insider trading".

The alleged breach relates to Hochtief's purchase of shares in Australian building firm Leighton in early 2014 and its extension of the last day on which shares could be purchased from January to February, ASIC said.

It alleged that Hochtief, the major shareholder of Leighton, was aware at the time that the Australian company's financial results for 2013 -- to be released that February -- were "likely to be at the high end of previous earnings guidance".

"Hochtief AG has admitted the alleged contravention," the ASIC said in a statement.

Hochtief said it had been cooperating with the ASIC's investigation since August 2014 and that it gained no trading profit from the alleged breach.

"Hochtief will submit to the court that its contravention was inadvertent," it said in a statement.

"By its contravening conduct, Hochtief did not seek or obtain trading profit."

Leighton, which is now called CIMIC Group Limited, reported its results on February 20, 2014, a move which saw its stocks close 4.88 percent higher, the ASIC said.