The suicide bomber struck as a car full of officers entered the compound of police headquarters in Karabulak at about 8.20 am local time (0950 IST), Russia's investigative committee said in a statement.
The attacker's explosives were spiked with "incapacitating elements" designed to inflict maximum injuries, it said, in a likely reference to metal shrapnel.
The bomber died at the scene and over a dozen police officers with injuries from the blast were rushed to hospital, where two of them died, the statement said.
The fresh attack came after a wave of suicide bombings, including two attacks on the Moscow metro that killed more than 50 Russians last week and two suicide strikes in Dagestan which claimed 12 lives.
The suicide blast was followed half an hour later by second explosion as police carried out a controlled explosion of a car bomb found fitted with a timer device.
The suicide bomber had been trying to enter the police station premises, when guards stopped him forcing him to detonate his explosives prematurely, investigators said.
Had the bomber managed to break into the police station the casualty figures would have been higher as there were about fifty traffic policemen gathered inside for morning briefing.
The suicide attacks, blamed on Chechen rebels, has prompted the government to promise tougher measures against the Islamist insurgency in the North Caucasus.
With today's killings, so far 12 people have died including local police chief and eight police personnel in Ingushetia, interior ministry was quoted as saying by news agency ITAR-TASS.
Acting prosecutor of the Caucasian town was among the injured of the second blast on Monday, Interfax quoted a source involved in the investigations.
Meanwhile, 81 injured in last Monday's twin attacks in Moscow are still undergoing treatment in hospitals, Health and Social Development Ministry said in a statement.
Scores of Muscovites were seen today laying the flowers on the tables on the platforms of Lubyanka and Park Kultury metro stations to pay the tributes to the people who died last week in the terror strikes.
Manwhile, a media interview by a Dagestani man that his daughter was involved in the attack on Park Kultury metro station, 40 minutes after the first attack at Lubyanka, has created confusion, as it does not fit into the investigations theory, which has already identified another woman.
In an interview to Novaya Gazeta" weekly one Rasul Magomedov identified his daughter Mariyam Sharipova, a village schoolteacher, as the attacker at the Park Kultury.
While on Friday the investigation had formally identified 17-year-old Jannat Abdurahmanova (Abdulayeva), born in 1992 in Khasavyurt, also in Dagestan, as the attacker.
According to Russian media, Abdurahmanova was the widow of Dagestani militant Umalat Magomedov (Al-Bar), who was killed during a special operation on December 31, 2009, after he shot at police who were attempting to search a car he was travelling in.
Investigations into Mariyam's involvement in the terrorist attack at Lubyanka are currently underway.
If Mariyam is confirmed as the attacker, the police theory that the two suicide bombers travelled to Moscow by bus from Kizlyar will be called into question.
The long distance bus takes 36 hours from Kizlyar to Moscow, but Mariyam was with her parents in Dagestan 1600 km away during the day on the eve of the Moscow attacks.
So far the investigation has not commented on Magomedov's claims although blood samples and other biological material have been taken Mariyam's parents for DNA analysis.
Image: Firefighters put out a fire at the site of a bombing in Karabulak | Photograph: Kazbek Basayev/ Reuters