Lebanon's army on Monday deployed in Hezbollah's southern Beirut stronghold taking over checkpoints in a deal struck with the Shiite group which has been accused of running a "state within a state".
Hezbollah leader Hassan Nasrallah welcomed the move in a televised address and urged local residents to cooperate.
Troops and security forces began entering the area in the afternoon, taking over checkpoints set up by his Shiite militant group after two car bombings in the southern suburbs since July.
"We welcome this step and greatly appreciate this national decision taken by state officials," Nasrallah said.
"We hope that the state and its officials carry out their national and legal duties towards all of Lebanon's regions," he added.
He called on residents of the group's stronghold, and those passing through it, to show "cooperation and respect" for the security forces and their measures.
Around 1,200 Lebanese troops and security forces began deploying in the mainly Shiite southern suburbs, where Hezbollah normally keeps a tight grip on security.
An AFP journalist at the scene said the deployment was taking place in stages, with Hezbollah members still visible at some checkpoints on side streets in the late afternoon.
The security points were established after car bombings in the southern suburbs that killed 27 people on August 15 and wounded more than 50 on July 9.
Following the bombings, Hezbollah turned the southern suburbs into a fortress with guards in civilian clothes policing the streets, stopping and searching cars, and asking motorists for their identity cards.
Nasrallah said Hezbollah's investigations into the second attack, in the Rweiss neighbourhood, showed Sunni extremists affiliated with the Syrian opposition were behind it.
"We have reached conclusive results, as promised," he said.
"It is a takfiri group working within the framework of the Syrian opposition and located on Syrian soil," he added, saying both Lebanese and Syrian nationals were involved in the attack.
"I think that (Lebanese) official security forces have reached the same conclusion," said Nasrallah, whose group has fought alongside regime forces in the Syrian conflict against mostly Sunni rebels.
Hezbollah has always kept a tight grip on its Beirut stronghold, but its security apparatus became increasingly visible after the attacks, raising tensions.
There were multiple incidents with citizens and journalists at the checkpoints, and a clash at one with Palestinian refugees earlier this month left one dead and four injured.
Interior Minister Marwan Charbel told AFP that after the army deployment: "No one else will be authorised to be present at the checkpoints... The state must extend its control over all Lebanese territory."
Charbel toured the southern suburbs as the deployment began and stressed it was being carried out "with coordination between the state and all parties."
Analyst Paul Salem, director of the Carnegie Middle East Centre, described the deployment as "positive," but said Hezbollah would retain control over security decisions that affect it.
"It takes decisions on major security matters in the country without consultation... It is an independent strategic player and moves without regard for the will of the state or Lebanese public opinion," he said.