The pair were convicted "in connection with their efforts to purchase one million dollars worth of high-powered weaponry for the Liberation Tigers of Tamil Eelam," the statement added, using the formal name for the separatist group.
Sarachandran, 30, pleaded guilty earlier this month to providing "material support to terrorism" by "conspiring and attempting to acquire guided surface-to-air missiles and missile launchers."
Yogarasa also pleaded guilty to providing material support.
The pair were arrested in 2006, after engaging in negotiations with an undercover FBI agent to purchase and export heat-seeking missiles, ten missile launchers, 500 AK-47s, and other military equipment.
"The defendants were acting at the direction of senior LTTE leadership in Sri Lanka," the Justice Department said, adding the group intended to use the missiles to shoot down Sri Lankan military planes.
The Tamil Tigers have fought for an independent homeland in Sri Lanka since 1972, but were dealt a deathblow in a war last year in which thousands of civilians were killed, according to United Nations estimates.Government troops killed the LTTE leadership and declared the total annihilation of the separatist guerrillas on May 18, ending Asia's longest running ethnic conflict.