The army is sending an anti-terrorism unit to Medellin, center of Colombia's drug trade, to halt assassinations of police by drug lords, the defense minister said in statements published Friday. Police said four more policemen were murdered Thursday on the streets of Medellin, Colombia's second-largest city. Their deaths bring to 123 the number of Medellin law officers murdered this year. Also Thursday, police said they arrested a drug trafficking suspect in Bogota wanted for trial in the United States. Julion Enrique Rojas, 49, has been accused by a Florida court of cocaine distribution and illegal possession of arms, judicial police spokeswoman Omayra Patino said by telephone. Defense Minister Oscar Botero said in a statement the army is sending its Mobile Brigade to Medellin to reinforce the city's 4,000-member police force. In less than six months, authorities have been forced to send an additional 1,300 troops to the city in the face of an unprecedented campaign of bombings and assassinations by the powerful Medellin cocaine cartel. Last week the army dispatched 350 more soldiers to Medellin from the elite Rifle Battalion. In a statement sent to the Medellin daily newspaper El Colombiano, Botero admitted that so far efforts to halt the violence have been insufficient. ``Social solidarity and national unity are what is needed to regain peace and harmony among Colombians,'' Botero wrote to the publisher of El Colombiano, which has harshly criticized the government's attempts to bring law and order to Medellin. Police Thursday began a new anti-drug crackdown in the city, stepping up detentions, searches and street patrols. In a 24-hour period, security forces arrested at least 86 people suspected of involvement in assassinations of policemen, the radio networks RCN and Caracol reported Friday, citing police sources. A judicial police report said the Medellin cartel is offering $4,300 to anyone who kills a policeman. Botero said that aside from troop reinforcements, authorities are installing a new helicopter base in Medellin to be used in the fight against the drug-related violence. The drug war began in August 1989 after drug lords assassinated a presidential candidate. Since then, the government has extradited 14 drug suspects to the United States, killed Medellin cartel leader Gonzalo Rodriguez Gacha, and confiscated hundreds of properties belonging to the cocaine magnates. They have responded with a bombing and terror campaign.