Nine Chechen policemen have been killed when militants attacked their vehicle in Russia's neighbouring republic of Ingushetia, officials say.
Another nine police were injured near the village of Arshty, in one of the deadliest recent attacks.
The Chechen police were conducting joint operations against militants in the volatile region.
Last month, Ingushetia's leader was seriously wounded in an apparent assassination attempt.
Chechen President Ramzan Kadyrov has vowed a "cruel" revenge on those who tried to kill Inghushetia's President Yunus-Bek Yevkurov.
The vehicle the Chechen police travelling in came under grenade and gun fire at about 0840 local time (0540 GMT) on Saturday, officials say.
The militants opened fire from a nearby forest.
The Chechen police were travelling in a convoy of five vehicles.
It was not immediately known if there were any casualties among the attackers.
Islamist militants have been battling pro-Kremlin authorities and Russian security forces in a low-level insurgency in Ingushetia, Chechnya and also Dagestan in the Caucasus region.