* Moscow police on alert for attacks - spokesman
* Says metro protected, search for potential troublemakers
* Latest bomb blasts test Kremlin’s authority in Caucasus
By Dmitry Solovyov
MOSCOW, Aug 18 (Reuters) - Moscow police were on heightened alert on Wednesday after two bomb blasts hit Russia’s volatile North Caucasus, causing dozens of casualties and renewing fears of insurgent attacks in the heartland of Russia.
A decade after Russian forces defeated separatists who controlled Chechnya, the North Caucasus is plagued by an Islamist insurgency stoked by corruption, poverty and the ideology of global jihad.
The bomb attacks on Tuesday, in a city near a busy cafe and at a police border checkpoint, occurred in mainly Orthodox Christian provinces where violence linked to the insurgency is less frequent than in predominantly Muslim Chechnya, Dagestan and Ingushetia.
They came after twin suicide bombings killed 40 people on Moscow’s metro in March, the deadliest attack in the capital in six years.
"Moscow police heightened security at 2100 (1700 GMT) yesterday," a police spokesman said on Wednesday. "The measure is open-ended, until a special order lifts it."
The spokesman said a larger number of police will patrol the city’s streets, the metro "and other vital facilities that support Moscow’s life".
Traffic police would search trucks at checkpoints on highways leading into Moscow and unspecified "measures to detect those capable of or planning to carry out illegal acts to shake public order have also been put in place," the spokesman said.
On Tuesday, authorities said a car bomb ripped through the cafe in the city of Pyatigorsk, in the Stavropol region about 225 km (140 miles) north of Chechnya’s capital, injuring about 30 people — three of them seriously.
Pyatigorsk was chosen by the Kremlin last year to be the administrative centre of the new North Caucasus Federal District, a regrouping of the region’s provinces to include the Stavropol region in a bid to tackle growing violence.
Hours earlier, police said a suicide bomber killed a policeman and wounded three others at a checkpoint at the border between the Christian-majority North Ossetia province and mainly Muslim Ingushetia.
Moscow, a metropolis of over 10 million people, has repeatedly been a target for bomb attacks.
The morning rush-hour bombings in March turned the global spotlight on the North Caucasus, on Russia’s southern flank which includes the Black Sea resort of Sochi, the site of the 2014 Winter Olympics.
(Additional reporting by Mikhail Antonov and Amie Ferris-Rotman)