A car bomb exploded near a police vehicle in Russia's troubled North Caucasus region Friday, killing four police officers, witnesses and officials said.

The blast occurred in the center of Nazran, the main city in the violence-plagued Ingushetia region.

The bodies of three people, apparently police, could be seen on the ground before the area was cordoned off, and a fourth person was taken from the scene in an ambulance. Four police officers were killed, the Ingushetia branch of the Emergency Situations Ministry said.

According to the ministry's southern Russia branch, three to five other people, apparently civilians, were injured. The blast occurred after police responded to a call about a suspicious car, the ministry's press service said.

Witnesses said a police vehicle stopped near a parked car, and officers emerged and apparently asked a group of men playing cards nearby about the car. It exploded as the police were getting back into their vehicle, the witnesses said -- accounts that suggested the call could have been a trap to lure police to the car.

Attacks on law enforcement authorities are common in Ingushetia. They usually are attributed to Ingush militants or rebels from neighboring Chechnya, the site of two devastating wars since 1994 pitting Russian government forces against separatist rebels who have increasingly espoused militant Islamic ideology.

In an attack targeting civilians, gunmen burst into a home in Ingushetia earlier Friday and killed three members of a Russian-speaking teacher's family, the teacher and officials said.

It was the second such attack this summer and it deepened fears that Russians in the region were being targeted -- possibly to try to increase ethnic tension.

The assailants, possibly as many as three, entered Vera Draganchuk's home in the town of Karabulak shortly after midnight Thursday and fatally shot her husband and two sons, aged 24 and 20, Draganchuk and the Ingush Interior Ministry said. Draganchuk was unharmed.

When she heard her husband shouting, "I yelled for my son to jump out the window after me, and then jumped out myself," Draganchuk said. When she didn't see her son, she said, she returned to the house and saw one son dead inside and the other, along with her husband, in the yard.

"My daughter has gone on vacation at the seaside, so she was saved. But after this nightmarish night, our life cannot be called a life," she said.

Draganchuk said she did not see the assailants and did not know their motive.

On July 16, an ethnic Russian teacher and her 24-year-old daughter and 19-year-old son were found dead, apparently shot while they slept, in what authorities said may have been an ethnically motivated attack.

The republic's chief prosecutor, Yuri Turygin, said in televised comments that the two attacks were similar and may have been linked.

On Wednesday, Ingushetia President Murat Zyazikov said in Moscow that several suspects have been arrested in the July killings, some of them from neighboring republics in the North Caucasus. He said such killings were aimed "to make people disappointed and leave" Ingushetia.

The regional Interior Ministry said Friday's attack may have been aimed to frighten Russians and Ossetians, a mostly Orthodox Christian ethnic group concentrated in the neighboring republic of North Ossetia. Ingush and North Ossetians fought a territorial war in the early 1990s, and relations remain tense.

Turygin said another possibility was that the attack was revenge for the killing of a suspected militant Thursday by forces of the Russian Interior Ministry and the regional branch of the Federal Security Service.

A neighbor said the Draganchuk family was well respected.

"Not a single Ingush would want this to happen to this family or to other (Russian-speakers)," said the neighbor, who only gave his first name, Imran.

"The people who did this are those who want things here to develop like they did in Chechnya," he said, not specifying whether he meant militants or forces linked to the government.