More death threats against police in the US have been made following the killings of two NYPD officers over the weekend.

Daryl Lofton was arrested by Memphis Police after posting on Instagram his intention to go from New York to Tennessee to kill two officers.

His post read: "Good job. Kill em all I'm on the way to NY now#shootthepolice 2 more going down tomorrow."

The New York Post reported the man was released after saying he was drunk and was not serious.

Another man from Brooklyn threatened police on Facebook, which the NYPD is said to be investigating. An image of a police car was uploaded on the site but the exact wording was released by the police.

It comes as mourners gathered in Central Park to pay tribute to the two officers, Wenjin Liu, 32, and Rafael Ramos, 40, who were shot dead by Ismaiiyl Brinsley while they sat inside their car.

He warned his intention to kill via Instagram by posting: "I'm Putting Wings On Pigs Today. "They Take 1 Of Ours, Let's Take 2 of Theirs."

The authorities labelled the attack as targeted assassination.

Ramos' teenage son, Jaden, took to Facebook to express his enormous grief over losing his father.

"Today is the worst day of my life," he wrote.

"Today I had to say bye to my father. He was [there] for me everyday of my life, he was the best father I could ask for. It's horrible that someone gets shot dead just for being a police officer. Everyone says they hate cops but they are the people that they call for help. I will always love you and I will never forget you. RIP Dad."

Lucy Ramos, an aunt of Rafael, during one of the memorials, said she hoped "we can move forward and find an amicable path to a peaceful coexistence".

Brinsley who shot his ex-girlfriend, 29-year-old Shaneka Nicole Thompson, in the stomach hours before the two police killings, had a history of hatred towards police and had been arrested at least 19 times. He was reportedly so violent, his mother was afraid of him.

New York mayor Bill de Blasio ordered flags to be flown at half-mast across the city.