The US government has issued a global travel alert for its citizens.

It's warning them to avoid crowded places, saying attacks are being planned in several regions by groups like Islamic State.

The warnings are focused on the transport system - millions of American's will be travelling for thanksgiving on Thursday.

Transport police chief Polly Hanson says security is being stepped up at airports and train stations.

Meanwhile, The terror threat in Brussels will remain at its highest possible level until Monday at least.

But Belgium's prime minister says the city's schools and underground system will re-open tomorrow.

One of the main suspects from last week's attacks in Paris is believed to be on-the-run in Brussels.