DAKAR - Guinea-Bissau could "explode" within months unless the international community takes strong steps to stop Latin American drug cartels overrunning the poor West African state, a U.N. official said on Tuesday.

The impoverished former Portuguese colony has become a major transit point for deadly Colombian and Brazilian cartels smuggling hundreds of millions of dollars in cocaine each year into lucrative European markets.

"Guinea Bissau is going to explode unless we do something ... between now and the end of the year," said Amado Philip de Andres, deputy representative for the U.N. Office on Drugs and Crime (UNODC) in West Africa.

"It is going to explode and it will have a domino effect everywhere. It's not a problem of West Africa: it is a problem of Europe and it is a problem of Latin America," de Andres told reporters on the sidelines of an anti-terrorism meeting in neighbouring Senegal.

Colombian cartels have seized control of some of the isolated islands along Bissau's fragmented coastline. If these gangs are allowed to continue operating, it would be a signal to other criminal syndicates to swarm upon Bissau, creating a lawless narco-state, he said.

"How can it explode? ... Civil war, regional destabilisation against post-conflict countries which are already recovering, like Liberia and Sierra Leone, or how about these groups funding conflict in north of Ivory Coast? That's what they are looking for," de Andres said.

Pitted against well-organised and wealthy drugs mafias, the Guinea-Bissau police have only one functioning vehicle, a handful of rusty weapons and no prison to hold suspects.

De Andres said his office was urgently seeking $300,000 in funding to appoint a permanent representative in Guinea Bissau to draft a national anti-drug plan and to finance a rotating presence from Western anti-narcotics agencies.

Just under a fifth of all the seized cocaine smuggled by air into Europe last year came from West Africa, de Andres said.

A programme to combat drug cartels has been budgeted at $15 million but so far international donors have baulked at financing this. The programme would help Guinea-Bissau build its first prison and a forensic laboratory.

"Let's get involved now because otherwise it will explode and it will cost not $15 million but $150 or $200 million to take the country back," de Andres said. "We don't want peacekeeping."