Los Angeles International Airport police said Tuesday they were increasing security after a second dry ice bomb exploded and two others were found in a restricted area of the airport, The Los Angeles Times reports.

The dry ice bombs were found near a plane parked at Gate 148 (in the Tom Bradley International Terminal) after one of the devices went off at around 8.30 p.m. local time (11.30 p.m. ET) on Monday, according to airport police. There were no injuries or damage caused by the explosion.

"The focus is definitely in the restricted area, not in the areas where passengers have access," said Sgt. Karla Ortiz. "We want to make sure that that gets tightened up."

Police officials say here is no link between terrorism and the four bombs discovered over the last two days at LAX.

This is the second incident to occur at LAX - a dry ice bomb in a soda bottle exploded in an employee restroom in Terminal 2 at 7 p.m. local time on Sunday. No injuries were reported either day, but several flights were delayed on Sunday until about 8:45 p.m. and there was minimal disruption of airport activities on Monday. The FBI said the incidents are being investigated by the Los Angeles Police Department's criminal conspiracy division, according to Ortiz.

According to the LA Times, the devices -- bottles with dry ice inside, appeared to be outside the terminal near planes where employees such as baggage handlers and others work on the aircraft and its cargo.

The FBI was assisting the LAPD in the investigation into how the devices were placed in restricted areas at LAX.

What is a dry ice bomb?

"Dry ice bombs typically consist of a plastic bottle filled with water and solid carbon dioxide. As the carbon dioxide turns to a gas it expands and causes the bottle to burst. They are prohibited in California and several other states," NBC News reports.

While, airport spokeswoman, Katherine Alvarado described the bottles found Monday night as "harmless," airports can never be too careful or take too many precautions.

To ensure everyone's safety, a crew of cleaners had to be evacuated from the plane near where the bottles were placed.

The incident was clear by 9.45 p.m. local time, Alvarado said.

Ortiz adds that it's too early to talk about suspects or motives, but law enforcement sources told NBC News the incidents were probably a prank.

"We have to finish our investigations to find out what the cause was," Ortiz said. "We always do our best to prevent such incidents but we will be keeping our eyes peeled following these similar events."