COLOMBO, Sri Lanka (AP) _ Sinhalese militants have killed 13 Sinhalese people in attacks throughout the country in the past two days, police and military officials said today.

Also today, a bomb exploded in a passenger bus, injuring 15, the officials said. The attack took place in Matara, 85 miles south of Colombo.

The officials, who under briefing rules cannot be identified, said a police inspector and a government-sponsored food retailer were among 13 victims killed by Sinhalese militants since Tuesday.

They said those killed were either supporters of the governing United National Party or members of the People's Liberation Front.

The front, a radical Sinhalese group, has vowed to disrupt next month's presidential elections. The group has been blamed for more than 550 killings in the past 15 months. Members of the front have attacked the government of President J.R. Jayewardene because of its plans for ending a 5-year-old insurrection by Tamil guerrillas.

The front contends an Indian-sponsored accord signed by Jayewardene in July 1987 makes too many concessions to the Tamil ethnic minority. It says 47,000 Indian troops now deployed in Sri Lanka to disarm Tamil guerrillas under terms of the accord are violating the island nation's sovereignty.

Sinhalese make up 75 percent of Sri Lanka's 16 million people and control the administration and the military. Tamils comprise 18 percent.

Militant Tamils claim they need a separate nation to protect them from discrimination by the Sinhalese majority in culture, education and employment.

More than 8,500 people, mostly Sinhalese, have been killed since the Tamil rebellion started in 1983.