Washington, Aug 14 (IANS): Demonstrations over the killing of an unarmed black teenager have intensified in the US city of Ferguson in Missouri state, media reports said Thursday.

Police Wednesday fired teargas and rubber bullets to disperse hundreds of protestors gathered at the centre of Ferguson to demonstrate against the shooting of 18-year-old Michael Brown by a city policeman, The Guardian reported.

Although the protest was largely peaceful, heavily armed police officers advanced towards the protestors with armoured trucks after two glass bottles were thrown at their line. Sniper rifles were trained on the demonstrators as they protested with their hands up as a symbol of peaceful protest, the daily said.

Police also arrested two journalists, including one from the Washington Post. A camera crew from Al Jazeera America said they were fired upon with rubber bullets.

The White House said early Thursday that President Barack Obama had interrupted his vacation on Martha's Vineyard, Massachusetts, to be briefed by US Attorney General Eric Holder on the escalating clashes between police and demonstrators.

Ferguson, a predominantly African-American city of some 21,000 people northwest of St. Louis, Missouri, in midwestern US, has been turned into a virtual war zone since Brown was shot dead by the police Saturday, according to media reports.

Police have said the shooting followed an assault on the officer. But a friend who was walking with Brown said the 18-year-old was grabbed after declining a request to get on to the pavement, and then shot repeatedly as he tried to run away. The officer has still not been named by investigators.