Gerhard Schroeder has said the US has "no respect" for Germany after media reported that his phone had also been tapped during his term as Chancellor.

"Tapping the phone of a Chancellor - this clearly goes too far," Schroeder told the Bild newspaper on Wednesday (5 February).

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Earlier this week, Sueddeutsche Zeitung and the NDR broadcaster reported that Chancellor Angela Merkel was not the only German head of government to have her phone bugged by US intelligence services.

According to the two German media, the US surveillance on the then-chancellor Schroeder started in 2002 when he refused to join the military intervention in Iraq.

It later turned out that the main reason for the US-led war - weapons of mass destruction allegedly held by the Iraqi dictator Saddam Hussein - did not exist.

"The US has no respect for a loyal partner and the sovereignty of our country," Schroeder told Bild.

He criticised the "huge mistrust of the Americans for an ally who showed a high degree of solidarity," in reference to the German troops sent to Afghanistan in support of the US effort.

He said the German decision not to go into Iraq "has to be respected. And that applies to the US as well."

For his part, foreign minister Frank-Walter Steinmeier, who was at the time Schroeder's chief of staff, said he is not surprised that his former boss was spied on. He added that he always suspected the surveillance activities of America's National Security Agency (NSA) had stretched over a long period of time.

German justice minister Heiko Maas also weighed in on the debate, noting that spying on Chancellors "does not contribute in any way to preventing terrorist attacks."

He told Spiegel Online his government is still seeking a no-spy pact with the US, despite reluctance in Washington to sign up to such a promise.

"It seems that preserving security is for the NSA just a fig leaf for collecting data in an unhindered way," Maas said.

A spokesman for Chancellor Angela Merkel on Wednesday did not confirm the media reports on Schroeder, saying what matters is not so much that one or another Chancellor was a victim.

"It's about protecting the rights of German citizens. It's about trust, which is needed in a partnership," the spokesman said.

He added that Merkel continues to talk to the US about the issue and warned that if trust is broken, "there is less, not more security."