Washington, July 10 (IANS): Hours after security levels were raised following an anonymous threat at the police headquarters in the north Texan city of Dallas, the police have given the all-clear, media reports said.

Two days after the killing of five police officers by a black US army veteran Micah Johnson during a protest rally in Dallas, a nearby parking lot was searched on Saturday for a "suspicious person" but no one was found.

SWAT officers were earlier deployed at the main building, BBC reported.

Two deaths during the week of Philando Castile in Minnesota and Alton Sterling in Louisiana have led to nationwide protests against the killing of black men by the white-dominated police.

Dallas Police said its officials -- using dogs -- searched the parking lot but the hunt turned up nothing.

Earlier on Saturday, the Dallas Police Department heightened security after it received an anonymous threat against law enforcement across the city.

The police asked the media to stop all live feeds around HQ "for the safety of our officers", the BBC reported.

Johnson, who was himself killed during the assault, supported black militant groups who encouraged violence against police.

Dallas Police chief David Brown said Johnson had told a negotiator that he wanted to kill white people, especially police officials, because he was angry about the recent shootings of black men.

US President Barack Obama said the US was "not as divided as some have suggested" in the wake of the shootings involving African-Americans.

He said Americans of "all races, all backgrounds", including many of those who were protesting, were outraged by the Dallas killings.

Johnson, 25, who acted alone, was killed by remotely detonated explosives that were sent into a car park where he had taken refuge after the shootings.

He was a member of the US Army Reserve from 2009 to 2015 who had served in Afghanistan.

Bomb-making material, rifles and a combat journal were found at his home in the Dallas suburb of Mesquite.

A number of gun attacks involving police officials and civilians have occurred in other parts of the US in the aftermath of the deaths in Minnesota and Louisiana.

Leaders of the Black Lives Matter organisation have condemned the Dallas killings but said planned marches, including a "Weekend of Rage" in Philadelphia, will go ahead as planned.