The last two weeks have been unusually gruesome in Tijuana, Mexico.

Since May 13, severed heads have been found scattered across the border city — one on a highway, two more in a cooler near a popular children's museum, and another boxed near its headless victim.

The heads came with cartel messages left on public display that signal drug gangs are challenging the control on the border smuggling corridor enjoyed by the formidable Sinaloa cartel.

The messages suggest a band made of up remnants of the weakened Tijuana or Arellano Felix cartel is challenging the Sinaloans, along with help from a cartel based more than a thousand miles to the south — the New Generation gang from Jalisco.

The latest beheading victims were found in Playas de Tijuana last Thursday. Authorities retrieved the heads after multiple witnesses reported driving past bloody bags left along the highway that hugs the US border fence, heading toward the beach suburb.

On May 17, a man's head was found inside a cooler, along with a written message from members of organized crime. His decapitated body was found just meters away.

En Playas de Tijuana fotografiaron bolsas con cabezas humanas. Más detalles en Síntesis TV. Fotos de Moises Guzmán. — José Ibarra Amador (@JoseibarraBC)May 21, 2015

But the first gruesome find this month came on May 13, when two severed heads were found near Tijuana's interactive children's museum.

Those heads were also discovered inside a cooler, accompanied by narco-messages signed by professed members of the largely dismantled Arellano Felix cartel, which at the height of its power was responsible for importing 40 percent of the cocaine entering the United States.

"This is what will happen to all the fags who are with you," the note read, threatening members of the Sinaloa gang.

The region has been disputed since the near immobilization of Tijuana's Arellano Felix capos, who've been largely captured or killed in recent years, leading to a free-for-all for control of the coveted plaza, or smuggling base.

The Jalisco New Generation Cartel made its first appearance in Tijuana on April 5, hanging banners in the city announcing their arrival. The messages were jointly signed by a group calling itself the "New Generation Cartel of Tijuana," a previously unknown and unconfirmed group.

This suggests a union between the quickly expanding Jalisco New Generation cartel, which is currently terrorizing western Mexico, and the once powerful Tijuana cartel. Yet Baja California state authorities have attempted to deny the scenario is taking shape.

"They are using titles like the New Tijuana Cartel, the Jalisco Cartel, and the Jalisco New Generation Cartel — as if the cartel in Jalisco has become allied with the one in Tijuana," a member of the state security commission told the Tijuana-based newspaper ZETA in April. "We are just beginning our investigation."

Authorities this week rejected reports of a possible incursion from the Jalisco group in Baja California.

"We've detected a cell with several members, but the cartel itself hasn't reached this border," Adrian Garcia, a spokesman for Baja California's security secretary, told VICE News on Tuesday.

As Tijuana struggles to shake its reputation as a city crippled by cartel violence, citizens are hoping this most recent spate is not a return to the bloodshed seen at the height of the struggles over the local plaza in the last decade.

Agent Gary Hill in the San Diego office of the Drug Enforcement Administration told The San Diego Union-Tribune that the Sinaloa cartel is currently believed to control "both the plazas in Tijuana and Mexicali," the state capital.

Though violence has declined in Tijuana since 2009, this past month has resulted in more than four times as many murders as the beginning of 2015. In January, there were just 24 murders in the city, according to state figures, compared to reportedly more than 100 since the beginning of April as a result of cartel violence.

"The past years have been very calm, surprisingly calm," a politically active lawyer in Tijuana told VICE News, requesting anonymity. "All I know is that the Jalisco cartel is entering, and they are here to take out whoever gets in their way."

It remains unclear what the scope of the Jalisco New Generation Cartel's foothold is in Tijuana, if any, but authorities claim they have already identified those responsible for the recent violence and do not believe that this cartel poses a wider threat to Tijuana's 1.3 million people.

"We are very far from reaching anything close to 2007, 2008, 2009, which I lived through in my own flesh," Tijuana's security secretary Alejandro Lares Valladares said on Friday.

"Everything is under control," he added.