"Prime Minister Netanyahu came to Moscow," Medvedev told CNN. "He did this under a closed regime, this was his decision. I don't understand what this was connected with, but sometimes our partners decide it this way," he added, offering no details.
Some experts say the two sides have been edging toward a wider strategic compact for some time.
"One of the key goals of the Netanyahu government is to establish a strategic partnership with Russia," says Yevgeny Satanovsky, president of the independent Institute for Middle East Studies in Moscow. "It's possible that such a relationship could become as important for Israel as its bond with the US."
Cooperation between Russia and Israel has grown in recent years, including recent Russian arms purchases from Israel, and many former Soviet Jewish emigrés have returned to Russia to take advantage of exploding job opportunities and the apparent easing of anti-Semitism in the country.
Russian missile sale would 'signal war'
No one knows for sure what was discussed in the high-level meetings between Israeli and Russian leaders, but experts say the only subject that would warrant such urgent top-level shuttle diplomacy is Russia's outstanding contract to provide ultramodern S-300 air-defense systems to Iran.
The latest version of the weapon, known as the "Favorit", can simultaneously engage 12 targets flying at any altitude from about 30 feet to 20 miles, and strike them at a range of up to 75 miles away.
Russia and Iran signed a contract for the weapons two years ago, but Russia has yet to deliver.