Iran on Wednesday slammed "inappropriate interference" by Germany and France following their condemnation of Tehran for its seizure last week of two Greek-flagged oil tankers in Gulf waters.

"Such inappropriate interference in the independent judicial processes of our country will not help resolve the issues," Iranian foreign ministry spokesman Saeed Khatibzadeh said in a statement.

Iran's Revolutionary Guards seized the Greek tankers in the Gulf on Friday, days after Athens confirmed it would deliver Iranian oil it had seized from a Russian tanker to Washington.

The German and French foreign ministries, in separate statements, condemned the seizure as a violation of international law, and called on Iran to immediately release the ships and their crews.

Berlin considered Iran's action "an unjustifiable interference in commercial shipping and therefore constitute a severe violation of international regulations."

Paris stressed its "commitment to the rules of international law protecting the freedom of navigation and maritime safety" and called on Iran "to immediately cease its actions that contravene these rules".

Khatibzadeh rejected "the issuance of such one-sided and unjustifiable statements".

He added that France and Germany "are protesting against the legal measures taken in Iran while remaining silent in the face of the illegal seizure of the Iranian-flagged ship by the Greek authorities and the unloading of its cargo."

The Revolutionary Guards -- the ideological arm of Iran's military -- had said it seized the tankers "due to violations", without elaborating further.

Greece has condemned Tehran's detention of the two ships as "tantamount to acts of piracy" and warned its citizens not to travel to Iran.

One of the tankers had been sailing in international waters, while the second was near the Iranian coast when it was seized, it added.

Nine Greeks are among the crews, the Greek foreign ministry said, without specifying the number of other sailors on board.

Iran said Saturday the crews of two tankers were in "good health" and not under arrest.