U.S. Energy Secretary Ernest Moniz was headed to Geneva Saturday to join talks with Iranian officials as efforts for an historic nuclear deal stepped up a gear.

It was the first time that Moniz, who is himself a nuclear physicist, had joined the negotiations, although U.S. energy officials have been involved in the intensive technical talks under way ahead of new meetings between the countries' top diplomats on Sunday and Monday.

Shiite Arab militias have flooded into northern Iraq's Kirkuk region to help Kurdish forces battle the Islamic State group, but their uneasy alliance threatens to reignite a much older conflict over the oil-rich area pitting the largely autonomous Kurds against the Arab-led government in Baghdad.

All across Iraq, the rapid advance by the Islamic State extremists over the past year has drawn longtime rivals into reluctant alliances. The shared struggle could with time help Iraqis forge a long-elusive sense of national unity. But it also risks papering over disputes that could burst into the open if the threat subsides.

Iranian Foreign Minister Mohammad Javad Zarif and top U.S. diplomat John Kerry will meet in Geneva this weekend for talks on Tehran's nuclear program, an Iranian official said Thursday.

Iran and world powers are trying to strike a deal that would prevent Tehran from developing a nuclear bomb, a goal it denies having, in return for an easing of punishing economic sanctions.

Tens of thousands of people demanding justice marched in symbolic silence Wednesday in soaking Buenos Aires to mark a month since the suspicious death of a prosecutor who was ready to accuse the Argentine president of a massive cover-up.

"I am here because I want to see justice done for someone who gave his life for the truth," said teacher Marta Canepa, 65, among those traipsing the 1.7 kilometers (just over a mile) under the banner "Homage for Prosecutor Alberto Nisman."

The White House on Wednesday denied keeping Israel in the dark over ongoing nuclear negotiations with Iran, but suggested its ally had cherry-picked information to bolster opposition to the deal.

Amid strains in the U.S.-Israeli relationship over negotiations to reach a landmark nuclear agreement with Iran, White House spokesman Josh Earnest rejected suggestions Israel was being frozen out.

Hundreds of Iranian students protested Wednesday in Tehran against the murder of three Muslim American students in the United States by a white neighbor last week.

Shouting "Death to America" 200-300 students linked to the bassiji Islamist militia demonstrated outside the Swiss embassy, which represents U.S. interests in Iran, an AFP correspondent said.

Argentina's President Cristina Kirchner Wednesday faces her first mass protest -- a silent march to be led by prosecutors and opposition leaders -- over the mysterious death of a prosecutor who accused her of a cover-up in a 1994 bombing.

As many as 300,000 people were expected to turn out for the march, marking one month since the unexplained death of prosecutor Alberto Nisman in a case that has ignited a political firestorm in Argentina.

Iran's ultra-conservative weekly "9-Day" was banned on Monday for criticizing the government over its negotiations with world powers on the country's controversial nuclear program, the ISNA news agency reported.

The state body charged with monitoring the media ruled that the paper had published articles "insulting towards the Imam (Islamic republic founder Ayatollah Ruhollah) Khomeini and against the regime's nuclear policy", the agency said.

Iran has denied reports that supreme leader Ayatollah Ali Khamenei wrote to U.S. President Barack Obama in response to an October letter mooting cooperation against the Islamic State group.

The Wall Street Journal reported on Friday that Khamenei, who has the final say in all matters of state in Iran, had sent a secret but noncommittal letter to Obama in response to his overture.

China is against another extension of the deadline for Iran to reach a deal with world powers in talks on its nuclear program, Foreign Minister Wang Yi said in Tehran Sunday.

"They have been extended twice, we hope that they will not be for a third time," Wang said at a joint news conference with Iranian counterpart Mohammad Javad Zarif.