Four people were killed and four others wounded when gunmen on Wednesday boarded a bus and opened fire on workers and passengers near El Salvador's capital city.

The bus driver, a fare collector and two riders died in the incident, which came just a week after a string of bus attacks brought service to a halt, the Associated Press reported. The murders appear to be linked to the rampant gang violence that is increasingly spiraling out of control in the Central American country.

El Salvador has seen record homicide numbers throughout the year, and authorities believe that the attacks mark a deliberate attempt by criminal organizations to ramp up pressure on the government of President Salvador Sánchez Cerén, who has refused to negotiate with the country's powerful street gangs.

Both gang-on-gang violence and attacks on police and common citizens spiked after Sánchez, who took office in June 2014, upped the ante by sending gang leaders to maximum-security prisons and encouraging police to use their weapons without fear in the line of duty or in defense of lives, according to the AP.

Bus transport all across El Salvador had been suspended last week for four days after eight bus drivers had been killed in shootings and the gangs had issued additional threats, Reuters recalled. However, the service had resumed by Friday under heavier guard by police and military units.

The latest attack occurred in Cuscatlan department, about 13 miles northeast of San Salvador, according to the AP. In San Juan Nonualco, southeast of the capital, meanwhile, police reported that an officer was killed in an ambush while patrolling the rural municipality.

Former New York Mayor Rudy Giuliani in June counseled El Salvador's leaders to forcefully go after the two groups in order to quell violence and restore order in the increasingly unstable Central American country.

"The biggest problem in New York was the mafia and then drug traffickers, but here it's two major gangs, and these two gangs need to be annihilated," Giuliani insisted, Reuters noted.