Defense officials from the United States and Russia held a video conference Wednesday to discuss safe flight operations over Syria, the Pentagon said.

"Progress was made during the discussions, which were professional and focused narrowly on the implementation of specific safety procedures," said the Pentagon in a statement.

The brief statement, however, provided no further details.

The latest round of military contacts between the two sides came days after US and Russian aircrafts came within visual range of each other during one mission on Saturday.

To avoid air accidents over Syria during their airstrikes against the extremist group the Islamic State (IS), the United States and Russia were currently engaged in talks aimed at ensuring "deconfliction" of air operations in Syria.

US defense chief Ash Carter said on Wednesday the United States would not cooperate with Russia's airstrikes in Syria, calling the airstrikes a "misguided strategy."

"This is a fundamental strategic mistake, one that will inflame and prolong the Syrian civil war," Carter said in a speech to the Association of United States Army. "We have not, and will not, agree to cooperate with Russia so long as they continue to pursue this misguided strategy."

Russia began airstrikes in Syria on Sept. 30 after weeks of military buildup inside the Arab country, which was scrambling to deal with a civil war and insurgency of the IS.

While the Kremlin insisted that its goal in Syria was to target the IS, Washington accused it of targeting rebels who opposed the Syrian government.

Despite Carter's dismissal of the Russian strategy in Syria, the United States on Friday announced it would abandon its own train-and-equip program in Syria, a central pillar of President Barack Obama's counter-IS strategy which was previously aimed at recruiting 5,400 Syrian rebels each year for three years.

Instead, the Obama administration would from now on support existing rebel groups.

The change is a recognition of the failure of Obama's flagship anti-IS training program after a testy congressional hearing in September by US General Lloyd Austin, who oversees the war against the IS, revealed that only "four or five" US-trained Syrian rebels currently remained in fight in Syria.

Later, the Pentagon corrected the number of US-trained Syrian rebels currently fighting the IS in Syria to nine.

The Pentagon admitted on Sept. 25 that the US-trained Syrian rebels gave about a quarter of US weapons to an al-Qaida affiliate in Syria.