In response to a “disturbing” trend of violence and theft in the past few weeks on and around the Yale campus, University and New Haven police are instituting expanded security measures, University Police Chief James Perrotti said in an e-mail to the Yale community Thursday.

Three robberies occurred in a span of 17 minutes on the night of Aug. 31, according to a New Haven Police Department press release. The victims in all three robberies described their assailants as three black males on bicycles, all wearing dark clothing, with one in possession of a small handgun.

Yale Police, with the help of New Haven Police, were able to apprehend two of the three assailants that night — both were minors.

The first incident, an attempted robbery, occurred at 10:13 p.m. at the intersection of Whitney Avenue and Cottage Street. Ten minutes later, as a man and woman were walking near Whitney Avenue and Lawrence Street, the woman’s purse and cell phone were stolen. The third incident took place in the area of 170 Linden St.

The purse and cell phone taken in the second incident were recovered by police, as well as a BB gun that looked like a semi-automatic weapon.

The first minor was charged with robbery in the first degree, larceny in the second degree, threatening in the second degree and carrying a dangerous weapon. He was also charged with conspiracy and criminal attempt on all charges. The other was charged with robbery in the first degree, larceny in the second degree and conspiracy on both charges.

One of the minors declined to comment and the other could not be reached for comment.

According to Perrotti’s e-mail, both University and New Haven police patrols have been increased in affected areas and more blue phones will be installed.

University Police Lt. Michael Patten said the Yale Police Department has also been discussing new security measures with Yale Security as well as adding to existing ones.

“We will be mixing officers on bikes, walking officers and plainclothes officers to target bad areas,” Patten said.

In addition to police measures, Perrotti said Yale students should be particularly careful in the area of Lake Place behind the Payne Whitney Gym, where the fraternities Alpha Delta Phi and Delta Kappa Epsilon are located; around the Divinity School campus both on Prospect Street and Whitney Avenue near Canner Street; and in the vicinity of Howe Street near Edgewood Street, where many students live off campus.

Two other incidents have occurred on Howe Street already this semester. Thomas DeLong DRA ’07 was shot in the hand in an attempted robbery near the intersections of Elm and Dwight streets, and Yale lab assistant Ashley Norman was assaulted in her building Sept. 1, near the intersection of Howe and Edgewood streets.