Berlin (AFP) - Former German chancellor Helmut Kohl has lashed out at his successors again in a new book coming out this week, blasting their policies on Russia and the euro.

Just weeks after being quoted as belittling his protege Angela Merkel as having been unable to "eat properly with a knife and fork" when she started out in politics, Kohl launched fresh attacks in excerpts printed Sunday in the weekly Frankfurter Allgemeine Sonntagszeitung.

The 84-year-old elder statesmen known as the father of German unity says the centre-left government of Gerhard Schroeder, his immediate successor from 1998 to 2005, made crucial missteps in allowing debt-mired Greece into the eurozone and bending the fiscal rules of its stability pact.

These two decisions "are among the gravest mistakes that we in the EU and the euro area" saw in recent years.

"What happened here is really a disgrace in German politics and at the same time a betrayal of German-French cooperation which should never -- as happened here -- been allowed to be used against the stability pact."

The pact was left in tatters after EU finance ministers in 2003 agreed to effectively suspend the rules for France and Germany, despite their repeated breaches of its ceiling for public deficits.

Kohl, the longest serving German chancellor, dismissed any criticism of his part in setting up the euro common currency, calling it a "tight clamp holding Europe together".

He is to present the book, titled "Out of Concern for Europe," in Frankfurt on Monday with European Commission chief Jean-Claude Juncker.

It hits a sour note ahead of celebrations on November 9 of the 25th anniversary of the fall of the Berlin Wall, which paved the way to German unification a year later.

In a chapter on Russia, Kohl also criticises Western leaders for "isolating" Moscow during the Ukraine crisis.

The decision by the Group of Seven club of rich nations to hold a summit without Russia in June was "drastic and depressing."

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"The West must, just as much as Russia and Ukraine, be careful not to squander everything that we achieved in the past," Kohl said.

Kohl has filed suit against a separate book published last month based on over 600 hours of taped interviews that he conducted with a journalist who was meant to ghost-write his memoirs before the project was scrapped.

In it, Kohl belittles the role of protesters in the fall of the Berlin Wall and rips into Merkel.