US and Russia sign deal to avoid Syria air incidents
Russia and the US have signed a deal that they hope will avoid clashes between their air forces in the skies over Syria, officials from both countries said.
Russian began air strikes in Syria on 30 September, saying it was targeting Islamic State (IS) militants.
Last week, the US said both countries' planes "entered the same battle space" and came within miles of each other.
Officials had been seeking an agreement since late September.
Pentagon spokesman Peter Cook said the text of the deal would remain secret at Moscow's request, but that it laid out means for both sides to communicate and establish a hotline on the ground.
The two countries would not, however, share intelligence on their targets, he said.
Mr Cook also said the deal ensured aircraft would stay a "safe" distance from each other, but he would not confirm if specific distances were agreed.
Last week, the Pentagon said Russian and US combat aircraft were in visual contact with each other, 10 to 20 miles (15-30km) apart.
Russia's Deputy Defence Minister Anatoly Antonov said the memorandum "contains a number of rules and restrictions aimed at preventing incidents between American and Russian planes".
Analysis: Gary O'Donoghue, BBC News, Washington DC
This agreement has taken almost three weeks to hammer out and is of limited scope. It does not co-ordinate air strikes, targets or intelligence - it simply aims to prevent the aircraft from getting too close to one another.
In a statement, the Pentagon said the protocols would include maintaining professional airmanship, the use of specific communication frequencies and the establishment of a communication line on the ground. The latter is designed as a backup if all else fails.
The agreement only covers flights over Syria and does not address Turkish concerns over Russian infringements of its airspace.
Nevertheless, it should make the risk of clashes between coalition and Russian planes less likely - providing everyone sticks to it.
Western countries and Syrian activists say Russian planes have been hitting non-IS targets, a claim Moscow denies.
Russia said it began its aerial campaign against IS militants and other jihadist groups after a request for military help from its ally, Syrian President Bashar al-Assad.
US officials said they were given only an hour's notice when the first Russian raids took place.
On Monday, at least 45 people were reported killed in Russian air strikes in a rebel-held area of the north-west Latakia province.