Germany's Foreign Minister Frank-Walter Steinmeier on Wednesday warned of the risk of a US-Russian conflict breaking out over Syria, as he readied to travel to the region.

American and Russian planes are currently waging separate air campaigns over Syria targeting ISIS militants, although Washington and its allies have accused Moscow of targeting Western-backed rebels in order to prop-up the regime of President Bashar al-Assad.

Steinmeier -- who is to visit Iran, Saudi Arabia and Jordan in the coming days -- said he wanted to "urgently caution the US and Russia not to military engage in a way that in the end could lead to a conflict" between them.

"Secondly, we must strive to help build bridges between Iran and Saudi Arabia so that it becomes conceivable that in the end we can get all the regional partners we need at one table," he said.

"For that I'll travel to Iran and Saudi Arabia next weekend."

Steinmeier leaves late Friday for Tehran to hold talks with his counterpart Mohammad Javad Zarif and President Hassan Rouhani. He will then travel on to Saudi Arabia before heading to Jordan, where he is due to join an OSCE Mediterranean Conference.

As the two separate air campaigns continued, US and Russian officials were on Wednesday to hold new talks on avoiding incidents in the skies over Syria, after the Pentagon said American and Russian planes had come within kilometres (miles) of each other on Saturday, making visual contact.