New York: Within minutes of President Bush giving 48 hours ultimatum to President Saddam Hussein, the US has raised terrorism alert from an "elevated" to "high", in response to intelligence reports warning terror attacks.

The security around sensitive sites, including tunnels and bridges, monuments, was put on high gear and visibility of police and security personnel have been tightened.

The Department of Homeland Security said a large volume of reporting across a range of sources, some of which are highly reliable, indicates that al-Qaida probably would attempt to launch terrorist attacks against US interests claiming they were defending Muslims or the Iraqi people rather than Saddam Hussein's regime.

The Department said there are many recent indications that al-Qaida is planning attacks using chemical, biological and radiological materials.

Dubbed as "Operation Liberty Shield", it will increase security at borders, strengthen transportation sector protections, enhance security at critical infrastructure, increase public health preparedness and ensure that all federal response assets can be deployed quickly.

PTI