Customs officials at Domodedovo airport in Moscow have seized six kilogrammes of heroin from a courier arriving from the Central Asian state of Tajikistan.

The officials say the seizure -- worth more than one-million dollars -- is the largest in five years.

Six people have been arrested; officials have identified five of them citizens of Tajikistan.

Correspondents say the country has become one of the major drug routes from Afghanistan to Russia and Western Europe.