In the wake of the deadly serial bomb blasts in Mumbai, the US and Britain on Wednesday issued travel advisories for their nationals, asking them to have "high level of vigilance" and exercise "extreme caution" while travelling.

"Although there is no indication so far that the attacks targeted Americans, the American Consulate General advises that Americans avoid crowds and demonstrations and exercise caution in areas where Americans and other expatriates generally congretate," the advisory issued by the US Embassy said.

"American citizens travelling throughout India should exercise extreme caution when travelling right now. Americans should exercise particular caution on trains, buses, or other forms of mass transit," it said pointing out that the blasts occurred on trains and railway stations.

US citizens were also advised to be wary of any unattended packages or other suspicious-looking items and asked to "maintain high level of vigilance and take appropriate steps to increase their security awareness".

In a similar advisory, Britain asked travellers to the country to exercise "increased vigilance" in the wake of blasts in Mumbai.

It said British Deputy High Commission in Mumbai is liaising with the local authorities and hospitals to see if any British nationals have been caught in the blasts.

Britishers were also advised against travel to or through rural areas of Jammu and Kashmir [Images], other than Ladakh, and all but essential travel by air to Srinagar [Images].