(BERLIN) - German President Horst Koehler will not complete his country's ratification of the EU's Lisbon Treaty until its highest court has ruled on legal challenges to the text, his office said Monday.

The presidency said Koehler has decided to heed a request from the Constitutional Court not to add his signature to the embattled reform treaty pending its ruling.

"The president is respecting the request of the Constitutional Court," his office said in a statement.

The adoption of the Lisbon Treaty is being challenged by The Left, a radicial left-wing opposition party, and a member of the ultra-conservative Christian Social Union.

The court has not yet set a date to rule on the challenges.

The upper house of the German parliament approved the Lisbon Treaty on May 23 before passing it on to Koehler for his signature -- which is usually a formality. The lower house passed it in late April.

Nineteen nations have ratified the embattled Lisbon Treaty in parliament, most recently Britain.

But Irish voters rejected the treaty in a referendum on June 12, sending the EU into a new constitutional crisis as all 27 member states must approve the text before it can enter into force.

Ireland was the only EU member to hold a referendum.

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