KABUL, Afghanistan - Twelve NATO soldiers, seven of them American, were killed in separate attacks Monday on the deadliest day of the year for foreign forces in Afghanistan. A U.S. civilian contractor who trains Afghan police also died in a suicide attack.

The bloodshed comes as insurgents step up bombings and other attacks ahead of a major NATO operation in the Taliban stronghold of Kandahar that Washington hopes will turn the tide of the war.

Five of the NATO deaths - all Americans - occurred in a single blast in eastern Afghanistan, Col. Wayne Shanks, a U.S. spokesman, said without giving further details. It was a grim reminder that the insurgents can strike throughout the country - not simply in the south, which has become the main focus of the U.S. campaign.

Two other U.S. service members were killed in separate attacks in the south - one in a bombing and the other by small-arms fire.

NATO said three additional service members were killed in attacks in the east and south but gave no further details. The French government announced that one of the victims was a sergeant in the French Foreign Legion who was killed by a rocket in Kapisa province northeast of Kabul.

Also Monday, two Australian soldiers were killed by an improvised explosive device in southern Afghanistan's Uruzgan province, the acting Defense Force chief, Lt. Gen. David Hurley, told reporters Tuesday.

The American police trainer and a Nepalese security guard were killed when a team of three suicide bombers attacked the main gates of the police training center in the southern city of Kandahar, U.S. officials said.

U.S. commanders have warned of more casualties as the alliance gears up for a major operation to secure Kandahar, the former headquarters of the Taliban.

The Afghan government is reaching out to the insurgents in hopes of ending the nearly nine-year-old war.

Last week, President Hamid Karzai won endorsement from a national conference, or peace jirga, for his plan to offer economic and other incentives to the militants to lay down their arms, and to seek talks with the Taliban leadership. The leadership has so far publicly shunned the offer, and the United States is skeptical whether peace can succeed until the Taliban is weakened on the battlefield.

Karzai's decision Sunday to replace two of the country's top security officials fueled speculation about divisions within the Afghan leadership over reaching out to the Taliban. The government said the two officials were replaced because of an armed attack on the peace jirga.

Both officials have a long background of opposition to the Taliban. Intelligence chief Amrullah Saleh was a senior figure in the Northern Alliance, which helped the United States oust the Taliban regime in 2001. Interior Minister Hanif Atmar served in Afghanistan's communist-era intelligence agency and fought mujaheddin opposed to the Soviet occupation.

In the wake of the shake-up, members of the former alliance, made up mostly of northern ethnic minorities, speculated that the changes were political and would weaken the security services.

"I would say it's a hasty and irrational decision by a president of Afghanistan who has deprived his own government of professional capacity to combat the insurgency," said Abdullah Abdullah, a key Northern Alliance leader and former foreign minister.

Karzai's spokesman, Waheed Omar, insisted the security lapse was the only reason for the resignations.

U.S. Defense Secretary Robert M. Gates, speaking to reporters on his way to London, said the security posts were for the Afghans to decide.

"I would just hope President Karzai will appoint in the place of those who have left people of equal caliber," Gates said. U.S. officials had singled out Saleh and Atmar by name as examples of competent leadership in a government riven by corruption and patronage.