The European Commission has ordered the partially privatised German post office to repay the 572m euros ($547m; £366.7m) it received in state aid.

The amount is one of the biggest ever ordered to be repaid by the Commission, which has found Deutsche Post in breach of competition rules twice in two years.

The ruling sends a strong warning that other EU postal services must be willing to compete with the private sector and not rely on state help.

Deutsche Post has vowed to challenge the ruling in the European Court of Justice, the EU's highest court.

Commitment to fight

"We cannot understand the ruling and find it highly questionable," said a spokesman for the group.

"We will fight the decision with all legal means possible and are confident of winning the case."

The Commission claims Deutsche Post used state funds to finance its attempts to undercut private sector rivals in the package delivery market between 1994 and 1998.

In March 2001, the commission fined Deutsche Post 24m euros for abusing its market position.

The German government, which holds a 69% stake in the postal firm, has two months to say how it intends to recover the money.

Deutsche Post shares fell 2.6% on the German stock market following the ruling.