NEW YORK (AFP) - Police in New York said on Friday they were ramping up security measures out of an "abundance of caution" following the mass shooting in Dallas that left five officers dead.

Patrolmen will travel in pairs, city police commissioner William Bratton told a news conference, while the unarmed auxiliary police will not be deployed in the streets.

Bratton said there were "no specific threats" against the New York Police Department (NYPD).

The events in Dallas "could happen in any American city, town, anytime," said Bratton, adding that law enforcement faced an "incredible challenge" due to the volume of firearms circulating in the United States.

Five police officers were killed on Thursday in Dallas and seven others wounded by at least one sniper who told police negotiators he had wanted to kill white cops following the deaths of blacks at the hands of law enforcement.

Bratton also warned against disorder during any demonstrations, vowing to arrest all those who break the law.

Before the Dallas attack, more than 1,000 people had held peaceful demonstrations until late in the evening in New York to protest against the killing of two blacks earlier in the week in Louisiana and Minnesota, according to police.

The NYPD said they had detained about 40 people, mainly for blocking traffic.