Russian President Dmitry Medvedev told Mitt Romney on Tuesday to use his head and stop reverting to Hollywood stereotypes after the U.S. presidential hopeful branded Moscow as Washington's top foe.

"I recommend that all U.S. presidential candidates, including the candidate you mention (Romney), do at least two things," Medvedev told Russian reporters on the sidelines of a nuclear security conference in Seoul.

U.S. President Barack Obama and Pakistan's Prime Minister Yousuf Raza Gilani vowed Tuesday to rescue a troubled anti-terror alliance which almost ruptured over 10 months of mistrust and recriminations.

The leaders met on the sidelines of a nuclear security summit in Seoul, in the highest-level exchange between the two sides since the killing of Osama bin Laden in a clandestine U.S. raid on Pakistani soil last May chilled ties.

World leaders including U.S. President Barack Obama on Monday began a two-day summit in South Korea aimed at curbing the threat of nuclear terrorism, organizers said.

The leaders or top officials from 53 countries, plus Interpol and three other international organizations, officially began the event with a working dinner hosted by South Korean President Lee Myung-Bak.

A U.S. delegation walked out of a regional conference in Tajikistan Monday after Iranian President Mahmoud Ahmadinejad lambasted U.S. policy on Afghanistan as the source of all the country's troubles.

Ahmadinejad launched his new tirade against Washington at a conference in the Tajik capital Dushanbe attended by leaders of Afghanistan's neighbors as well as a U.S. delegation led by Assistant Secretary of State Robert Blake.

U.S. President Barack Obama met his Chinese counterpart Monday for talks expected to focus on North Korea's upcoming rocket launch, a day after a blunt appeal to Beijing to get tougher with Pyongyang.

Obama and President Hu Jintao held talks before the start of a nuclear terrorism summit in South Korea which has been overshadowed by the North's planned launch in mid-April.

The top U.S. diplomat for the Middle East heads to Sanaa on Sunday to meet senior government officials and activists amid a political transition after longtime ruler Ali Abdullah Saleh stepped down.

The United States on Saturday warned U.S. citizens against traveling to Mali due to current "instability" after a military coup in the West African country.

"The situation on the ground remains fluid and unpredictable," cautioned the State Department in the travel warning, saying "law and order is not assured" in the wake of the unrest.

Patients with advanced heart disease who received an experimental stem cell therapy showed slight improvements in blood pumping but no change in most of their symptoms, U.S. researchers said Saturday.

Study authors described the trial as the largest to date to examine stem cell therapy as a route to repairing the heart in patients with chronic ischemic heart disease and left ventricular dysfunction.

India, which is rapidly expanding its atomic power program, said Saturday that nuclear terrorism is a "continuing concern" ahead of a summit on atomic safety to be held next week in Seoul.

The summit will focus on the threat from nuclear-armed terrorists and follows one in Washington convened by U.S. President Barack Obama in 2010 on the same subject.

U.S. Secretary of State Hillary Clinton gave the green light Friday to resume $1.3 billion in annual military aid to Egypt despite fears it is slipping in its avowed transition to democracy.

The move marked the denouement of a crisis in the 30-year-old U.S.-Egyptian alliance that erupted over a crackdown in December on pro-democracy groups by Egypt's interim military rulers.