Wildlife campaigners in Mozambique say police have cracked an ivory poaching ring believed to be responsible for the deaths of at least 39 elephants.
The Wildlife Conservation Society said six suspects were arrested in Niassa National Reserve at the weekend, in what is seen as a major breakthrough in the anti-poaching fight.
The head of the group, which manages the park, Cristian Samper hailed "strengthened security and intelligence" for the arrests, in a country experiencing an ivory poaching crisis.
Those arrested were Mozambican and Tanzanian nationals.
Twelve tusks valued over $150,000 (115,000 euros) were found in their possession, according to authorities from the US-based organisation.
A 2011 count indicated that there were 12,000 elephants in the park, making it one of Africa's most important populations.
The WCS estimates that poachers killed 1,000 elephants last year and another 500 so far this year.
The park is "on the front line of the crisis in ivory," Samper said.
The remote park is twice the size of South Africa's Kruger National Park and poachers have to hike for days to reach it.
Poaching in Mozambique had for a long time gone unpunished, until the enactment of legislation criminalising big poaching in June this year.
Under the law, convicted poachers face up to 12 years in jail.
The country is also in the process of re-training rangers who often come under fire from heavily armed poachers.
Environmentalists say they are working with authorities to gather intelligence about the entire ivory trafficking network from local buyers right the way to markets in the East.
Last year the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) singled out the southern African country as one of the world's worst in combating poaching, and threatened it with sanctions.