Fireworks were canceled in downtown Brussels, Belgium, where police last week detained 14 people suspected of plotting to help an accused al-Qaida militant break out of jail.
Festivities in Paris centered on the famous Champs-Elysees avenue and the Eiffel Tower, where about 4,500 police and 140 rescue officials patrolled the streets.
In Thailand, an army spokesman said he believed that five bombs set off by suspected Muslim insurgents in a Thai-Malaysian border tourist town likely targeted New Year's revelers. The bombs, which wounded 27 people, exploded in the hotel and nightlife area of Sungai Kolok, spokesman Col. Akara Thiprote said.
Baghdad witnessed something Iraq had not seen since before the invasion of 2003 - people publicly partying to welcome in a new year.
The ballrooms of two landmark hotels - the Palestine and the Sheraton - were full of people for New Year's Eve celebrations. After years of car bombings, mortar fire and suicide attacks, Iraq's capital was sufficiently calm to warrant the two high-end parties in the once-posh hotels.
Several European countries rang in the new year with new habits.
The smoke-filled cafe became a thing of memory in France. Following up on a ban last year on smoking in many indoor locations, cigarettes were prohibited in dance clubs, restaurants, hotels, casinos and cafes.
Fabienne Simon, a 27-year-old smoker, said the ban was "not that bad."
"There is nothing better than to go to a nightclub, a coffee place where there are no cigarettes," she said. "You come out, it's great, you aren't smelling of cigarettes."
Two European Union newcomers, Cyprus and Malta, start using the euro at the stroke of midnight. The Mediterranean islands, both former British colonies, scrap the Cyprus pound and Maltese lira to bring the number of countries using the shared currency to 15.
In France, President Nicolas Sarkozy gave the first traditional New Year's greeting of his presidency, with a "message of hope, faith in life and in the future." In Russia, Vladimir Putin delivered the last New Year's Eve address of his eight-year presidency, boasting of economic improvements and claiming to have restored a sense of unity among Russians, who are likely to see him stay in power as prime minister after he steps down in a few months.
In Moscow, thousands gathered in Red Square to watch a concert beneath the colorful onion domes of St. Basil's Cathedral, and fireworks above.
Along with the innovations, old traditions were maintained.
Revelers in New York converged on Times Square to watch the dropping of a new energy-efficient ball. More than 300,000 people were expected to crowd the Las Vegas Strip and downtown resorts for the countdown to midnight.
In London, people were gathering in Trafalgar Square and along the banks of the River Thames to watch a fireworks display and hear Big Ben - Parliament's iconic bell - welcome the New Year with 12 resounding bongs.
In a quirky tradition in Spain and other Spanish-speaking countries, Madrid residents dine on 12 grapes - one for each chime at midnight.
Berlin held a massive fete: In a stretch leading from the city's famous Brandenburg Gate along Tiergarten park to the western part of town, officials set up three stages, 13 bands, 40-yard tall Ferris wheel and over 100 beer stands and snack joints.
In Vatican City, Pope Benedict XVI took a somber note, lamenting what he called the "trivialization" of sexuality and lack of faith among young people during a vespers' service in St. Peter's Basilica.
In Asia, China started its Olympic year with a New Year party including fireworks, singing and dancing put on by the organizers of the Summer Olympics.
In Sydney - one of the first cities to celebrate the New Year - one million revelers cheered as fireworks sprayed from the iconic Harbor Bridge. Fireworks displays were being repeated at the stroke of midnight in cities around the world.
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Associated Press writers around the world contributed to this
report.
