Across the border tonight, Nuevo Laredo police and Mexican soldiers are on high alert after a grenade was launched into a municipal police substation. It happened less than a block from city hall around eight o'clock tonight. No one was killed or hurt in the incident. A police cruiser was blown up but other than that there was only minor damage. It comes as Nuevo Laredo has seen several weeks of rest from the bloodshed and violence. Authorities say it's unclear if drug traffickers carried out the attack. Officers and soldiers are stepping up patrol on the streets until further notice.