Merkel pledged her unwavering support for the Jewish state 60 years after it was founded in the aftermath of the Nazi Holocaust, as she on Tuesday became the first German head of government to address the Knesset.
Newspaper editorials welcomed Merkel's expression of shame for the murder of six million European Jews during World War II and her criticism of the Hamas movement's rocket attacks on Israel and Iran's threats against the country.
But they warned that Germany's hopes to play a constructive role in the Middle East peace process could be hobbled by a stance seen as too pro-Israeli, with only muted criticism of some of the state's more contentious policies.
"Germany must be careful not to make (US President George W.) Bush's cardinal mistake and be biased in the peace process," the centre-left daily Süddeutsche Zeitung wrote.
"Merkel must maintain her independence and criticize Israel directly for its occupation and settlement policy. A genuine friend tells the truth."
The mass-selling tabloid daily Bild, itself a longtime defender of Israel, said Germans must be aware that Merkel's expressions of unwavering solidarity may require the country to come to Israel's defence one day.
"In Israel, Merkel's speech will not be forgotten. Anyone so clearly declaring themselves a friend and ally of Israel must know that this will be taken literally when the time comes, and that Germany cannot duck the situation if things get tougher in the Middle East or if Iran really does get serious about the nuclear bomb," it said. "Merkel should speak openly about this. She must explain how far Germany would be prepared to go (and why) to secure Israel's existence."
The centre-right daily Frankfurter Allgemeine Zeitung also cautiously warned against making hollow promises to Israel.
"It cannot be overlooked that the means Germany has of supporting Israel's security are limited," it said. "It doesn't have the United States' influence in the Middle East, and in international policy it is only a medium-sized power."
Merkel's three-day trip to Israel with several of her cabinet ministers marked the start of regular governmental consultations between the countries, a framework for talks that Germany has only with a handful of close allies.
Israeli Prime Minister Ehud Olmert welcomed Merkel's tough stance on the Iranian nuclear programme after talks with her and said she had told him "any threat to Israel's security is a threat to Germany's security."