The murder rates in four US major cities have risen to levels not seen for two decades, analysis has shown.

Although overall violent crime has decreased in the country by at least 50% since the early 1990s, Milwaukee, Memphis, Chicago and Baltimore saw considerable rises. Other cities in the country saw similar increases, analysis by the Wall Street Journal showed.

The report noted that Los Angeles and New York, the two largest cities, continued a long term drop. Baltimore has the highest homicide rate so far this year with 47 killings in the first seven weeks of the year.

Chicago has seen an increase on the same period last year. Last year, the second city's rate of 27.8 killings for every 100,000 residents was the highest since 1996.

That may buoy US President Donald Trump who repeatedly references Chicago as a reason for new policies toward law enforcement. However he he has been called out for embellishing some statistics, at one point falsely claiming the Chicago murder rate to be at its highest in 47 years.

The largest police union in the country was one of the few groups that endorsed Trump during the presidential campaign. A criminologist told the WSJ said that "local drug markets" were a factor, while some communities had stop cooperating with law enforcement.

Milwaukee's police chief said that issues surrounding high profile shootings of black men had left officers worried they could become the next viral sensation, saying that when the police officers "feel like they are being treated as the enemy, it affects their motivation".

Although other cities which have seen similar high profile shootings have not seen the same spike in violence. Police chiefs in Los Angeles and New York said their focus on good relations with local communities was the main factor for their cities' lower statistics.