The price of ivory has shot up and can fetch more than $1,000 per kg
Kenyan authorities have seized almost 700kg of ivory worth millions of dollars in a night-time raid at the country's main airport.
The Kenya Wildlife Service says a similar amount was intercepted in the Ethiopian capital, Addis Ababa.
Both consignments - with a potential value of more than $1.5m (£938,000) - were reportedly headed for Thailand.
The BBC's Will Ross in Nairobi says poaching is on the increase mostly owing to high demand for ivory in Asia.
Our reporter says it is not yet clear whether the ivory, recovered at Nairobi's Jomo Kenyatta Airport, had been trafficked from other parts of the continent or was from East Africa.
Twenty years ago the world's elephant population was plummeting and the trade in ivory was banned.
But over the past decade the ban has been periodically relaxed and occasional supervised ivory auctions have been allowed.
Officials say the sales have fuelled demand for ivory in Asian countries, especially China, contributing to a sharp increase in elephant poaching.
So far this year poachers in Kenya have killed 128 elephants for their ivory; last year 98 were killed.
In July, Kenyan authorities intercepted 16 elephant tusks and two rhinoceros horns being illegally exported to Laos from Mozambique.
Some wildlife experts have attributed the increase in elephant poaching to the presence of Chinese workers in Africa.
With demand for ivory products increasing back home, some Chinese workers on low salaries in Kenya are reported to have become middlemen in the ivory trade.
And because of the high demand for ivory across Asia, the price of ivory has shot up and can fetch more than $1,000 a kilo.