New Delhi - In the aftermath of bombings in the key Indian cities of Bangalore and Ahmedabad, various countries have warned to their citizens to exercise a "high degree" of caution while travelling in the country.

The US government appealed to its citizens travelling or residing in India to be watchful in the backdrop of the terrorist attacks, the IANS news agency reported Thursday.

"American citizens are encouraged to maintain a high level of vigilance, remain aware of their surroundings, monitor local news reports, avoid crowded places, and take appropriate steps to bolster their personal security," a special advisory said.

Besides the US, many other countries, including Australia, Britain and Canada have issued similar travel alerts to their citizens, the report said.

"We advise you to exercise a high degree of caution in India because of the high risk of terrorist activity by militant groups," said an advisory from the Australian government's Department of Foreign Affairs and Trade.

"Cities such as New Delhi, Mumbai, Hyderabad, and Varanasi may be placed on heightened alert by local authorities at short notice. An increased police presence and tighter security restrictions may be imposed any time," an advisory by the Canadian government said.

Meanwhile, the Japanese embassy in Delhi received an email warning of bombings at a popular Sarojini Market in the city, a spokeswoman said. This prompted the mission to close its consular section on Thursday and ask Japanese citizens to avoid crowded places.

But the Delhi police said the email was a hoax and was sent by a man who was denied a visa by the embassy.

Bangalore and Ahmedabad were hit over the week-end by nearly 30 synchronized bombings that killed at least 52 people.

While on Friday Bangalore was targeted with eight blasts which killed two people and injured six others, the next day Ahmedabad was rocked by 21 coordinated blasts, which claimed at least 50 lives and wounded 160.

Since Sunday, many metropolitan cities across the country reported a large number of hoax calls even as police found and defused 21 bombs in Surat, located some 200 kilometres south of Ahmedabad.

A Muslim militant group calling itself the "Indian Mujahideen" claimed responsibility for the Ahmedabad bombings and has threatened more attacks.

The group claimed the attack was in revenge for the 2002 Hindu Muslim riots in Gujarat in which 1,000 people, mostly Muslims, were killed. (dpa)