Prosecutors dropped assault charges against George Zimmerman stemming from a domestic dispute involving his girlfriend last month, a Florida State Attorney said on Wednesday.

The case against Zimmerman, who was acquitted this summer in the fatal shooting of unarmed black teenager Trayvon Martin, fell apart after his girlfriend, Samantha Scheibe, withdrew a domestic violence allegation, Seminole-Brevard State Attorney Phil Archer, said in a statement.

The sheriff's department had probable cause to arrest Zimmerman at the time of the incident, Archer said.

"However, upon reviewing the recent affidavit ... and taking into account the conflicting statements about what occurred, the failure to co-operate with the ongoing investigation, and a lack of any other corroborating evidence or witnesses, there is no reasonable likelihood of successful prosecution," Archer said.

Zimmerman, 30, was arrested Nov. 18 after he allegedly pointed a shotgun at his girlfriend during a domestic dispute at the house in central Florida he shared with her.

Faced 3 charges

Zimmerman faced three charges including aggravated assault, a felony, as well as two misdemeanours, domestic violence battery and criminal mischief.

Scheibe, 27, told police that at one point during a verbal altercation Zimmerman grabbed a shotgun and pointed it at her, broke a glass table and pushed her out the door.

He then barricaded the door with furniture, police said. Scheibe suffered no injuries during the incident.

Zimmerman, a former neighbourhood watch captain, was acquitted on July 13 of murdering Martin as the 17-year-old walked back to the townhouse where he was staying after buying snacks at a nearby convenience store.

Zimmerman said he shot Martin in February 2012 in self defence. The shooting and trial polarized the U.S. public on issues of race, gun laws and self-defence laws.

Since his acquittal, Zimmerman has had several brushes with law enforcement officials. He has twice been stopped for speeding, once in Texas and in Florida.

In September, Zimmerman was questioned by police after his estranged wife called 911 saying he threatened her with a gun. He was not charged in the incident, which occurred a week after she filed for divorce.