Mexican security forces on Sunday killed seven more members of a presumed cartel assault force that rolled into a town near the Texas border and staged an hour-long attack, officials said, bringing the death toll to at least 21.The Coahuila state government said in a statement that lawmen were still chasing remnants of the force that arrived in a convoy of trucks and attacked the city hall of Villa Union on Saturday.Gov. Miguel Angel Riquelme said at least 14 people had died by that afternoon, four of them police officers. He also said then that several municipal workers were missing. It wasn’t clear if they had since been located.The new statement did not give a new death total, but said seven more attackers were killed on Sunday in addition to 10 who reportedly died the day before.The governor said the armed group stormed the town of 3,000 residents in a convoy of trucks, attacking local government offices and prompting state and federal forces to intervene. Bullet-riddled trucks left abandoned in the streets were marked C.D.N. – Spanish initials of the Cartel of the Northeast gang.The town is about 35 miles (60 kilometers) south-southwest of Eagle Pass, Texas, and 12 miles (20 kilometers) from the town of Allende – site of a 2011 massacre involving the Zetas cartel in which officials say 70 died.Videos of the shootout posted on social media showed burned out vehicles and the facade of Villa Union’s city hall riddled with bullets. Rapid gunfire could be heard in videos along with frantic people telling friends to stay indoors.The governor said security forces would remain in the town for several days to restore a sense of calm.Mexico’s murder rate has increased to historically high levels, inching up by 2% in the first 10 months of the presidency of Andrés Manuel López Obrador. Federal officials said recently that there have been 29,414 homicides so far in 2019, compared to 28,869 in the same period of 2018.The November slaughter by Mexican drug cartel gunmen of three women who held U.S. citizenship and six of their children focused world attention on the rising violence.