A bomb apparently hidden in a briefcase exploded Wednesday outside a top court in New Delhi, killing 10 people in the deadliest attack in the Indian capital in nearly three years.

The bombing, which came while the city already was under high alert, raised questions about India's ability to protect even its most important institutions despite a national security overhaul that followed the 2008 siege of Mumbai.

The government rallied Indians to remain defiant in the face of such attacks.

"We will never succumb to the pressure of terrorists," Prime Minister Manmohan Singh said during a visit to neighboring Bangladesh. "This is a long war in which all political parties and all the people of India will have to stand united so that this scourge of terrorism is crushed."

The bomb exploded about 10:14 a.m. near a line of more than 100 people waiting at a reception counter for passes to enter the court building to have their cases heard.

"There was smoke everywhere. People were running. People were shouting. There was blood everywhere. It was very, very scary," said Sangeeta Sondhi, a lawyer, who was parking her car near the gate when the bomb exploded.

The blast shook the courthouse, sending lawyers and judges fleeing outside, said Sanjiv Narula, a lawyer who was in the building.

People ran to the blast site to assist the injured, piling them into auto-rickshaws to take them to the hospital. Police said 10 people were killed and scores more injured. Ambulances and forensic teams rushed to the scene, along with sniffer dogs and a bomb disposal unit, apparently checking for any further explosives.

Renu Sehgal, a 42-year-old housewife with a case before the court, had just received her pass and was standing nearby with her uncle and mother while her husband parked their car when she heard the explosion.

"The sound was so huge and suddenly people started running," she said. "We were all in such a big panic. ... I'm lucky I survived."

The court building was evacuated after the blast. The High Court is an appeals court below India's Supreme Court.

There was no immediate claim of responsibility for the bombing, and Home Minister Palaniappan Chidambaram told Parliament the government had not identified the attackers.

"We are determined to track down the perpetrators of this horrific crime and bring them to justice," he said. The attack was carried out even though the capital had been on high alert because Parliament was in session, Chidambaram said.

The court bombing was the first major terror attack in India since a series of blasts in three busy Mumbai neighborhoods killed 26 people on July 13. Suspicion for those attacks fell on the shadowy extremist network known as the Indian Mujahedeen, though no one has been arrested.

The blast was the second explosion at the High Court this year. On May 25, a small explosion that appeared to be a failed car bomb erupted in the court parking lot.

The attack rekindled memories of the string of deadly bombings that rocked the country in 2008. But that violence had mostly abated after the November 2008 siege of Mumbai, when 10 Pakistan-based militants wreaked havoc across India's commercial capital for 60 hours, killing 166 people.

However, a series of smaller attacks raised concerns in recent months that the violence was returning.

Last Sept. 19, two gunmen on a motorcycle shot and wounded two Taiwanese men outside a famous New Delhi mosque. A few minutes later, a bomb rigged to a nearby car malfunctioned and caught fire. On Dec. 7, a bomb exploded in the city of Varanasi, killing a 2-year-old, and a few months later came a failed attack on the High Court in New Delhi.

Some analysts feared these attacks, culminating in the July attack in Mumbai, signaled an effort to regroup by the Indian Mujahedeen _ a domestic militant group blamed for many of the 2008 attacks.