SEOUL, South Korea — North Korea threatened today to retaliate against the U.S. and South Korea over sanctions imposed on the communist regime, a day after South Korea's president renewed his offer of conditional aid for the impoverished country.

The U.S. is moving to enforce U.N. as well as its own sanctions against North Korea to punish its second nuclear test in May and a spate of missile tests.

If the U.S. and South Korea "tighten 'sanctions' and push 'confrontation' to an extreme phase, the (North) will react to them with merciless retaliation ... and an all-out war of justice," said a North Korean military statement reported today by the country's official Korean Central News Agency.

The North's latest warning came in response to an annual computer-simulated war game Seoul and Washington that will kick off tomorrow.

CLINTON ASKS IRAN TO FREE U.S. CITIZENS

WASHINGTON — Secretary of State Hillary Rodham Clinton is pressing Iran to release Americans who are detained or have gone missing there.

Retired FBI agent Robert Levinson has been missing since March 2007. Three hikers — Joshua Fattal, Shane Bauer and Sarah Shourd — were detained by Iranian authorities on July 31. And an Iranian-American scholar, Kian Tajbakhsh, was arrested last month on charges related to provoking unrest.

Clinton's statement yesterday comes days after a U.S. graduate student held in Iran returned to Los Angeles.

The student, Esha Momeni, was imprisoned for a month because of her research on an Iranian women's rights movement.

3 IRAQI HERDERS KILLED IN MORTAR TRAINING

BAGHDAD — Three Iraqi men herding cattle were killed yesterday after wandering into the middle of a U.S.-Iraqi mortar training exercise north of the Iraqi capital, the U.S. military said yesterday.

American forces were conducting a live-fire training exercise with Iraqis near Taji, about 12 miles north of Baghdad, when the men walked onto the artillery range, the military said. An 11-year-old boy was also injured and evacuated to a U.S. military hospital where he was in stable condition last night, the military said.

ATLANTIC STORM WATCHES ISSUED

MIAMI — Tropical storm watches were issued yesterday for the U.S. and British Virgin Islands and other parts of the Leeward Islands as Ana raced west through the Atlantic.

Tropical Storm Bill, the second storm of the Atlantic season, formed farther east and forecasters said they expect it to become a hurricane over the next several days.

A tropical storm watch means tropical storm conditions are possible, usually within 36 hours.

The government of the Netherland Antilles issued a watch for St. Maarten, Saba and St. Eustatius. The governments of Antigua and Barbuda issued watches for the British Virgin Islands and Montserrat, Antigua, Barbuda, St. Kitts, Nevis and Anguilla.

MEXICO POLICE CHIEF ESCAPES ASSAULT

MONCLOVA, Coahuila — An ex-general serving as police chief of a northern Mexican city escaped an assassination attempt that killed three of his bodyguards, the latest attack on an official appointed to step up the fight against drug cartels.

Assailants in pickup trucks opened fire on Monclova police chief Juan Carlos Pacheco as he headed home Friday evening, a police statement said yesterday. Pacheco was not hurt but three of the police officers guarding him died.