Iran has vowed to retaliate against any attack, after Israeli Prime Minister Benjamin Netanyahu called on the world to draw a “clear red line” on Tehran's nuclear program.

Iran's deputy U.N. ambassador, Eshagh al-Habib, accused Mr. Netanyahu of making “baseless allegations” against Tehran, which insists its nuclear program is for peaceful purposes. World powers say Iran is seeking to develop nuclear weapons.

Speaking to the U.N. General Assembly Friday, German Foreign Minister Guido Westerwelle called on Iran to “stop playing for time.” He warned the “stability of the entire region is at stake” due to the unresolved dispute over Iran's nuclear program.

On Thursday, Mr. Netanyahu told delegates at the U.N. General Assembly that time was running out for the world to stop Iran. He used a drawing of a bomb to explain that a “red line” must be drawn before Iran completes the second stage of nuclear enrichment necessary to make a bomb.

U.S. President Barack Obama spoke by phone with Mr. Netanyahu Friday. The president reaffirmed the United States' “unshakeable commitment to Israel's security,” and both leaders agreed on the shared goal of preventing Iran from obtaining nuclear weapons.

U.S. Republican presidential candidate Mitt Romney also spoke with the Israeli prime minister Friday. He told reporters after the call that he does not believe military action will be necessary to prevent Iran from obtaining nuclear weapons, but said he cannot completely take the military option off the table.

Earlier this week, President Obama said the U.S. will do what is necessary to prevent Tehran from obtaining a nuclear weapon but he did not give Iran any ultimatums. U.S. Secretary of State Hillary Clinton met with Mr. Netanyahu late Thursday. Officials did not provide any details of the talks.

Also Thursday, representatives of the P5+1 group of nations – the United States, Russia, China, Britain, France and Germany – met on the sidelines of the U.N. General Assembly to discuss efforts to resume nuclear talks with Iran. A State Department official said the group “remains completely unified in wanting to get the Iranians to consider and to address the concerns of the international community, and that the P5+1 is completely united in ensuring that Iran does not acquire a nuclear weapon.”