Custom officials seized 638 pieces of illegal elephant ivory estimated to be worth $1.2 million at Kenya’s main port, evidence of what wildlife officials described Wednesday as a growing threat to East Africa’s elephants.

The ivory was in a container destined for Indonesia and was discovered late Tuesday, according to the Kenya Revenue Authority officer in charge of the port. The tusks were from Tanzania. Documents said the container was carrying slabs of decorative stones,

The seizure comes about a week after 12 elephants were killed in a Kenyan park and their tusks chopped off.

Elephant poaching is on the rise across Africa because of increased demand from Asia — particularly from China — for ivory trinkets. Poor African villagers can earn large sums for killing an elephant and taking its tusks.

Kenyan officials became suspicious of the container because shipping documents used similar descriptions and details as a shipping container full of ivory seized in Hong Kong earlier this month. That seizure, the third big seizure of ivory in three months, found more than a ton of elephant tusks worth $1.4 million. Customs officers seized 779 pieces of ivory weighing 1,323 kilograms (2,916 pounds).

Kenya Wildlife Officials said Wednesday that Kenya last year lost 384 elephants and 19 rhinos to poaching compared with 289 elephants and 29 rhinos poached in year 2011. The Kenya Wildlife Service arrested 1,949 poaching suspects last year.