"The contract was signed a few years ago but it hasn't been fulfilled yet," Putin said Tuesday at a news conference in the Russian city of Yekaterinburg. "We don't want to upset the balance in the region."
Putin’s comments followed news reports last week that quoted Syrian President
"It is not our policy to talk publicly about military issues in terms of what we possess or what we receive," Assad was quoted as saying.
Russia said last week that it planned to proceed with deliveries of the S-300 system, saying the missiles would act as a deterrent to "hotheads" determined to intervene in the Syrian conflict.
The announcement came after the
Putin said Russian arms sales to Syria "are carried out based on transparent, internationally recognized contracts."
"They don't violate any international provisions," he said Tuesday.
The various reports of new weaponry headed to Syria have complicated U.S.-Russian efforts to sponsor peace talks between the Syrian government and its opponents.
Putin reiterated that Russia was "dissatisfied" with the EU decision to relax the arms embargo on Syria and said the question of participation by the opposition in a proposed conference in Geneva should be resolved "as soon as possible."
"As is known, the Syrian leadership already officially declared its agreement to take part in the work," Putin said.
The most prominent opposition group, the U.S.-backed Syrian National Coalition, has said it will boycott the conference until pro-Assad Iranian and Hezbollah forces leave Syria.
Iran backs Assad but denies having any fighters in Syria. Hezbollah has acknowledged that its militiamen are fighting alongside the Syrian military in a battle for the strategic city of Qusair, near the border with Lebanon.