About 10,000 troops have surrounded the city of Soyapango in El Salvador as part of a massive crackdown on gangs, President Nayib Bukele announced.
All roads leading into the city have been blocked, and riot police have searched homes for gang members, the BBC reported.
Police also stopped anyone trying to leave the city and checked documents.
The operation is part of a major crackdown on gangs following a spike in violence earlier this year.
The country's Justice Minister said 12 people have been arrested so far.
Soyapango is one of El Salvador's largest cities, home to more than 290,000 people. The city, just 13 kilometers west of the capital, San Salvador, has long been known as a center of gang activity.
"As of now, the municipality of Soyapango is totally fenced off," President Bukele wrote on Twitter. "8,500 soldiers and 1,500 agents have surrounded the city, while extraction teams from the police and the army are tasked with extricating all the gang members still there one by one."
He added that ordinary people have nothing to fear, and said the crackdown was part of an operation against criminals, not against honest citizens.