New Delhi - At least 18 people were killed and over 50 injured as serial blasts ripped through three busy market areas in New Delhi on Saturday, officials and news reports said.

Police said five blasts took place in the city's crowded Ghaffar Market, Connaught Place and Greater Kailash areas within 40 minutes beginning at 6:15 pm (1245 GMT).

Confirming the deaths were the result of a terrorist attack, Federal Home Minister Shivraj Patil said, "I am told that 18 lives have been lost and many have been injured in five serial blasts."

Delhi police chief YS Dadwal said that a majority of the casualties were reported from Ghaffar Market and Connaught Place.

Delhi Mayor Arti Mehra told reporters: "It is a shameful and cowardly act. I appeal to everyone to maintain calm. (The terrorists) cannot kill the spirit of Delhi."

The NDTV network reported that two unexploded bombs were defused in the India Gate area, one of the highest security zones in the country and the Regal cinema hall in Connaught Place.

The blasts took place in busy areas that are crowded with shoppers on the weekend. Police immediately evacuated the areas and cordoned off the markets.

The city was placed on high alert as security was strengthened, and all markets in the city were ordered to shut.

A Muslim militant group Indian Mujahideen claimed responsibility for the attacks.

"In the name of Allah, the Indian Mujahideen strikes back once more," an e-mail entitled "Message of Death" sent by the group to Indian news outlets said.

"Do whatever you can and stop us if you can, exclusively from Indian Mujahideen," it said.

The same group had also claimed responsibility for serial bombings in May and July in the cities of Jaipur and Ahmedabad, where 119 lives were lost.

Indian police believe that the Indian Mujahideen is a "smokescreen" or front for the banned Students Islamic Movement of India.

At least 20 people were injured in the blast at Ghaffar market and were taken to the nearby Ram Manohar Lohia hospital, the PTI news agency reported.

Three explosions took place in the Connaught Place area, including at a central park and one near a metro station, in which at least 20 people were injured.

The bombs had been kept inside dustbins in the area.

The fifth low-intensity blast occurred in the Greater Kailash market.

Witnesses said they could hear deafening blasts, while television footage showed shattered window panes and mangled vehicles at the scene, as well as police and locals moving the injured into ambulances.

"It was a loud blast, and the earth beneath our feet trembled. There was dense smoke all around," a witness at Connaught Place said.

Pakistani President Asif Ali Zardari and Prime Minister Yousaf Raza Gilani strongly condemned Saturday's blasts.

In separate messages, the president and prime minister expressed their shock and grief over "the loss of precious human lives," according to the state-run Associated Press of Pakistan.

"The elements involved in such heinous act are enemies of humanity," Gilani said.

"The people and government of Pakistan share the pain, grief and loss of precious lives and property of the people of India," Pakistani Information Minister Sherry Rehman said.

Delhi has been a target for Islamic militant groups that have regularly carried out blasts in the city from the 1990s.

The terrorists have also carried out raids at the Indian Parliament and national monuments like the Red Fort in 2001 and 2000.

The last major attack on the Indian capital was on 29 October 2005 when 59 people were killed in serial blasts again targeting Delhi markets. (dpa)