The attack on India's parliament came at a time of heightened security in the wake of the attacks on the US and war in Afghanistan.

As such, it is bound to raise questions over whether the measures being implemented are adequate.

The attackers entered what is one of the most heavily-protected buildings in the country.

The incident has come as a huge embarrassment to the government which has been speaking in recent weeks of security threats against Indian targets, including a specific attack on parliament.

But India's Home Minister, LK Advani, rejected any criticism over security measures, saying it was very difficult to prevent such attacks.

"There is no breach of security. This appears to be a fidayeen (suicide squad) attack and even the Pentagon in the US was attacked by fidayeen," he said.

Security blanket

At the best of times, central Delhi - where most government offices are located and officials reside - resembles a fortress.

Policemen clutching carbines can be seen around official buildings, many inside specially erected watchtowers.

Ministers travel in armoured Indian-made Ambassador cars, escorted by specially trained commandos.

More than 200 paramilitary troops guard its perimeter, while its gates are manned by over 100 Delhi police personnel and the parliament's own security staff.

In addition, the MPs and senior ministers have their own personal bodyguards.

Critics point out, however, that while the ordinary public has to put up with the restrictions resulting from this extraordinary level of security, those in positions of authority are rarely challenged.

This may explain why the militants used a fake official car to enter the complex.

But other observers say that the measures in place are still not enough to prevent determined attackers.

KPS Gill, a retired police official who led the fight against Sikh insurgents in the late eighties, says it is difficult to prevent access to public officials.

"In any democratic society there is a balance between individual liberty and security," he told BBC News Online.

"Full proof security - where we close the access roads and take other such measures - is impossible," he added.

Anti-terror bill

Recently, the government has been trying to pass a controversial anti-terrorism bill through parliament.

The bill grants extraordinary powers to security forces to detain suspects and raid suspected terrorist hideouts.

But the opposition has argued that existing laws were more than adequate to fight terrorism, and that the new law could target minorities, especially India's 120 million Muslims.

The attack on parliament may give the government more leverage in its efforts to get the bill through.