"We are not the only ones in Europe who have a say over when such a tax should be implemented, but we will campaign for this with great vigor," Steffen Seibert told a regular news conference in Berlin.

A media report at the weekend that Merkel is not serious about implementing a European financial transaction tax threatens to undermine an initial deal struck last week with the opposition over the EU's planned fiscal pact.

Der Spiegel weekly reported on Sunday that Merkel's Chief of Staff, Ronald Pofalla, had said such a tax would not get passed in the current legislative period so the center-right coalition could support the idea in principle knowing it would not have to act on it any time soon.

But government spokesman Seibert said Merkel fully supported the idea and would campaign for it.

"The chancellor personally is convinced of the necessity of this and will raise this issue at a four-way meeting in Rome with Spain, France and Italy on June 22," he said.

"(French President) Francois Hollande can also be expected to support this issue."

(Reporting By Gareth Jones and Stephen Brown, Writing by Sarah Marsh)

• A Permanent Economic Emergency