They had fled across the border to Bangladesh amid heavy fighting between the Myanmar military and rebel insurgents in Rakhine
Meanwhile, RAB has arrested eight abandoned handmade bombs in the capital.
Fire service said a parked bus at the city's Shyampur was set afire around 2.30pm on Thursday.
"It was an empty bus and parked. So no one was injured. Two fire-fighting units rushed to spot and put out the fire," Fire Service Control Room in-charge Ataur Rahman told bdnews24.com.
In the city’s Hazaribagh, eight handmade bombs were found in front of a house, said RAB-2 Operations Officer Maruf Ahmad.
It is yet to be confirmed whether anyone has been arrested in connection with the recovery.