In a brazen assault, suicide attackers lobbed grenades and opened indiscriminate fire in a heavily-guarded local court in Pakistani capital, killing at least 11 people including a judge and many lawyers.

Unidentified gunmen burst into the court complex and opened fire, killing 11 people, including Additional Sessions Judge Rafaqat Ahmad Khan Awan and many lawyers.

At least 25 others were injured in the attack in F-8 area of the federal capital where a large number of expats stay.

Though the exact number of the attackers were not known, Islamabad police chief said two of the attackers blew themselves up when cornered.

"The two gunmen when challenged blew themselves up. This was a suicide attack," Inspector General of Police Sikandar Hayat told reporters.

"11 people are dead and 25 others injured of whom five are in serious condition," said Javed Akram, Vice Chancellor of Pakistan Institute of Medical Sciences.

He said all the injuries were due to gun shots on the upper part of the body. He said majority of the killed and injured were young lawyers.

Eyewitnesses said two young gunmen entered the court premises and threw two grenades. They opened indiscriminate fire with assault rifles which continued for about 15 minutes.

The attack comes just days after Interior Minister Chaudhry Nisar Ali Khan said Islamabad was a safe city.

This is the first terrorist attack in the heart of Islamabad in a long time.

A recent report of the Interior Ministry had said the threat perception was high in Islamabad and a number of sleeper cells are active here.

The Tehrik-e-Taliban Pakistan spokesperson Shahidullah Shahid, who had announced a ceasefire two days back, announced that his group was not involved in the attack.

Chief Justice of Pakistan Tassaduq Hussain Jillani took notice of the attack.

A three-member bench headed by the chief justice will hear the case regarding the attack tomorrow.

The Interior Secretary will also appear before the court along with Chief Commissioner of Islamabad and police chief.

The federal capital is heavily secured and is considered as one of the safest city in Pakistan. However, today's attack has put the security lapses under scanner.

Prime Minister Nawaz Sharif and Interior Minister Nisar condemned the attack. Bar Councils across Pakistan have called for a strike today to condemn the blast.