Rick Santorum Tuesday dropped his long-shot White House bid, effectively handing Mitt Romney the Republican party crown to challenge President Barack Obama in November elections.

"This presidential race is over for me," Santorum told supporters in Gettysburg, in his home state of Pennsylvania.

Israeli Defense Minister Ehud Barak on Sunday warned the six-power group negotiating with Iran to set stringent limits on its nuclear enrichment at forthcoming talks.

"If the P5+1 will set a much lower threshold, like just stop reaching 20 percent it means that basically the Iranians at a very cheap cost bought their way into continuing their military programs, slightly slower but without sanctions," Barak said in English in an interview aired on Sunday by CNN.

A stealth surveillance drone operated by the CIA penetrated deep inside Iran over three years ago, snapped images of Iran's secret nuclear facility at Qom and returned home, The Washington Post reported late Saturday.

The newspaper said that during that flight, analysts at the Central Intelligence Agency and other agencies watched carefully for any sign that the aircraft, called the RQ-170 Sentinel, had been detected by Tehran's air defenses on its maiden voyage.

With a White House meeting, talks at a think-tank, and interviews with newspapers, Islamists unshackled by the Arab Spring are launching a new charm offensive to reassure a nervous Washington.

The rise to power of elected Islamists in Tunisia, Egypt and elsewhere has alarmed many Americans, who fear the emergence of Iran-style theocracies that would deny the rights of women and minorities and antagonize Israel.

U.S. President Barack Obama called Iraqi Prime Minister Nouri al-Maliki Tuesday to congratulate him on the Arab summit held last week and to stress his support for a unified Iraq.

In a statement announcing the call, the White House termed last week's Arab summit, Iraq's diplomatic coming-out party following the full withdrawal of U.S. troops late last year, a "success."

Iran declared on Monday it will not be swayed from its nuclear "path" by sanctions, a week before talks with world powers that are increasingly seen as a last chance for diplomacy in its showdown with the West.

"The sanctions may have caused us small problems but we will continue our path," Foreign Minister Ali Akbar Salehi vowed in an interview with the official Islamic Republic News Agency (IRNA).

U.S. President Barack Obama called Saturday for higher tax rates on wealthy Americans, saying the current system of tax breaks for top income earners was unfair.

"Today, the wealthiest Americans are paying taxes at one of the lowest rates in 50 years," the president said in his weekly radio and Internet address.

South Korean officials said Saturday that they will continue working with the U.S. to reduce oil imports from Iran after President Barack Obama greenlighted potential sanctions against countries that continue to buy Iranian oil.

South Korea is one of several major importers of Iranian oil that have not received exemptions from the U.S. sanctions.

U.S. President Barack Obama gave the go-ahead for fresh sanctions against Iran's oil sector Friday, judging there is enough oil on world markets to ensure the move will not hit U.S. consumers.

With just hours to go before a legal deadline, Obama determined the United States could levy sanctions against banks and other financial institutions buying oil from Iran, without roiling markets.

A U.S. drone launched a missile attack on a militant compound in Pakistan's northwestern tribal region near the Afghan border early Friday, killing four insurgents, security officials said.

The missiles targeted a house in a market area of Miranshah, the main town in North Waziristan, known as a stronghold of Taliban and al-Qaida-linked militants, they said.