Police in Russia are hunting suspected Islamist militants after five people were found shot dead in cars, less than a month before the Sochi Olympics.
The victims, who include taxi drivers, were left inside four cars in the southern region of Stavropol. Two of the vehicles were booby-trapped.
Police sources named three suspects, all from the volatile neighbouring region of Kabardino-Balkaria.
Two are allegedly Islamist militants, already wanted over an earlier killing.
In another development, Russian media say a woman has been arrested on a bus in Stavropol in possession of a suicide bomb belt. There has been no official confirmation.
Two suicide bombers killed 34 people in the southern city of Volgograd on 29 and 30 December.
Russia has mounted the biggest security operation in the history of the Olympic Games for Sochi, 300km (186 miles) south of Stavropol.
The shooting victims were found near the villages of Tambukan, Zolskaya and Mariinskaya. The cars were said to be Ladas, commonly used as cabs in Russia.
When investigators approached one of the vehicles, an improvised explosive device went off close by but no-one was injured, police said. A second explosive device was made safe.
A counter-terrorist operation has been launched in the area.
Police sources told Russian media that three suspects were being sought: Anzor Margushev, 32, and his brother Artur, 23, as well as Vadim Shogenov, 25.
Artur Margushev and Mr Shogenov are both already on a federal wanted list for the killing of a hunter in Stavropol on 29 October.
At the time, investigators told the news website Caucasian Knot that both men were suspected of being members of an Islamist militant group, the KBK Vilayat.
Following reports on other Russian media, an unnamed law enforcement source told Komsomolskaya Pravda newspaper that a would-be suicide bomber had been caught on a bus in Stavropol after entering from the Karachayevo-Cherkessia region.
The woman, who was travelling with a small boy thought to be her son, was being interrogated by Russia's Federal Security Service, the source added.
Stavropol is particularly vulnerable to attack from Islamist militants in the North Caucasus as it borders the mainly Muslim regions of Chechnya, Dagestan, Kabardino-Balkaria and Karachayevo-Cherkessia.
Russia's most wanted man, Chechen rebel leader Doku Umarov, has urged his fighters to target the Winter Games.
About 37,000 police and interior ministry personnel are due to provide security for the Games, which open on 7 February.