-By Daniel Eagan

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Balancing hard-hitting action with buddy-cop humor, District 13: Ultimatum sticks close to the formula established in District B13 (2004). Disillusioned rebel Leïto (parkour expert David Belle) teams again with double-crossed cop Tomasso (Cyril Raffaelli) to save District 13, a walled-off Parisian slum, from nuclear annihilation. Pitched cannily at World Beat fans as well as martial-arts zealots, this Luc Besson production aims to please and nails its targets with more speed and style than most of its higher-priced competition.

Besson also wrote the script, which finds the French Secret Service collaborating with the evil Harriburton conglomerate to cleanse some valuable real estate the government had previously written off. Now controlled by five competing ethnic gangs, District 13 is a hotbed of crime and violence. When Roland (Pierre-Marie Mosconi) and other Secret Service agents frame gang leaders for the murder of two cops, the military has an excuse to deploy nuclear weapons.

Standing in their way: Leïto, first seen trying to bomb his way out of District 13, and Tomasso, introduced in drag during a drug bust. In a brilliantly choreographed sequence, Tomasso takes out dozens of bad guys and disarms a doomsday bomb while holding a priceless Van Gogh canvas. It's a breathless bit of derring-do that ranks with the best martial-arts fights of the past few years.

Arrested on trumped-up charges by Roland and his boss Walter Gassman (Daniel Duval), Tomasso seeks out Leïto's help. Breaking into and out of jail, the duo then have to broker peace among the five gangs before leading an assault on a heavily armed command center where Gassman and the French President (Philippe Torreton) are preparing their attack.

Backed by a pounding score, Ultimatum builds a teeming canvas for its leads, with location shooting in Serbia providing a suitably decayed look for the B13 slums. Besson establishes a fast-moving narrative, but has trouble engineering a convincing climax, falling back on impossible plot twists and tongue-in-cheek repartee. Overall this is still a solid entertainment, with engaging takes on culture clashes, modern economics and media mashups.

In fact, Ultimatum marks an almost complete upgrade over District B13: better fights, better supporting cast, less pointless sadism and perversion. Raffaelli, a memorable thug in Live Free or Die Hard, has improved tremendously since the original. His acting is much more persuasive, while his fighting and action choreography are world-class. Belle figures into an extraordinary chase down the outside of a high-rise apartment building, but stays in the background for much of the film.

District B13 director Pierre Morel has moved on to films like Taken and From Paris with Love. He's replaced by Patrick Alessandrin, better known in France for domestic comedies like Mauvais esprit (2003). Alessandrin handles the action chores here adroitly, but credit for District 13: Ultimatum really belongs to Luc Besson, perhaps the hardest-working man in the French film industry.