Visiting German Chancellor Angela Merkel said on Tuesday that it would not be acceptable to allow Iran led by President Mahmoud Ahmadinejad to get nuclear weapons.

"A nuclear bomb in the hands of an Iranian president who denies the Holocaust, threatens Israel and denies Israel the right to exist is not acceptable," Chancellor Merkel told U.S. lawmakers in a speech.

"Security of the state of Israel is, for me, nonnegotiable now and forever. .. Not only Israel is threatened, but the whole of the free world. Whoever threatens Israel also threatens us," said the German leader.

The United States, its European allies and Israel claim that Iran's nuclear program is aimed at developing nuclear weapons, while the UN Security Council also requires Iran to suspend its uranium enrichment activity.

However, Iran insists that its nuclear plan is only for peaceful purposes, and continues its uranium enrichment activity despite the pressure from the western countries and relevant resolutions and sanctions of the United Nations.

Merkel, who is here to mark the 20th anniversary of the fall of the Berlin Wall, is the first German leader to address U.S. Congress since Konrad Adenauer in 1957.

Earlier on Tuesday, Merkel met with President Barack Obama in the White House. The two leaders reaffirmed the U.S.-German alliance over a range of common challenges from climate change to nuclear non-proliferation.

Germany stands at the center of European affairs and is a key partner in U.S. relations with Europeans in NATO and the European Union. And as two of the world's leading trading nations, the United States and Germany share a common, deep-seated commitment to an open and expanding world economy.