Sergey Lavrov insisted the shipment complied with international law. He said the plane carried no weapons and that the "electric equipment for radar" was a legitimate cargo.
Mr Lavrov added, however, that the cargo was of "dual purpose," meaning it could have civilian and military applications.
Turkey's prime minister said it was carrying ammunition and military equipment for the Syrian Defence Ministry.
The US accused Russia of pursuing a "morally bankrupt" policy in Syria, following the seizure by Turkey of Russian radar parts.
The State Department said that it had "grave concern" that Russia is continuing to supply the Syrian regime with "serious military equipment", particularly because it is a member of the UN Security Council with presumed responsibilities for maintaining global security.
Russia says the parts are legal and denounced Turkey's interception of the plane.
But State Department spokeswoman Victoria Nuland said the only reason the shipment was legal was because Russia, along with China, has repeatedly blocked UN sanctions against Syria. She said it was "legally correct but the policy is still morally bankrupt".
www.mid.ru/brp_4.nsf/main_eng (Russian Foreign Ministry)