SAN SALVADOR El Salvador has deployed at least 5,000 soldiers and 500 police to surround a town in the northwest of the country in a push to arrest those responsible for the suspected gang killing of a police officer, President Nayib Bukele said on Wednesday.

The officer was killed while on patrol in Nueva Concepcion, some 42 miles (67 km) northwest of the capital on Tuesday in an attack by alleged gang members, security authorities said.

"Since early morning, we have established a security perimeter around Nueva Concepcion," Bukele wrote on Twitter, saying this would enable the "search for those responsible for the murder and the entire structure of gang members and collaborators still hiding there."

"They will pay dearly for the our hero's murder," added Bukele, who has faced criticisms from human rights groups for his authoritarian governing style and brutal crackdown on crime, particularly street gangs.

El Salvador has suspended constitutional rights in a so-called state of exception that allows police to swiftly arrest and jail suspected gang members while suspending their right to a lawyer and court approval of preliminary detention.

Over 68,000 suspects have been arrested since last year, and thousands transferred to a new "mega prison". Human rights groups say some innocent people have been caught up in the policy, including at least dozens who died in custody.

The policy is however credited with cutting high rates of violent crime and supported by the majority of the population, according to various polls.

Bukele's government has previously launched similar surges of security forces in urban areas considered highly dangerous in an attempt to stop drug trafficking and the movement of gang members.

(Reporting by Nelson Renteria; Writing by Sarah Morland; Editing by Alistair Bell)