Islamabad  - At least 22 people were killed and dozens more injured as an explosion ripped through a Shiite mosque Sunday in Pakistan's eastern province of Punjab, government officials said.

A suicide bomber blew himself up at the main entrance of the mosque in Chakwal district, some 90 kilometres south-west of capital Islamabad, when the security guards challenged him.

"At least 22 people are killed and more than 50 are injured, many of them critically," said provincial law minister Rana Sanaullah.

The district police officer BA Nasir told Express television that the death toll could be as high as 35. Some of the critically wounded were being transferred to Rawalpindi.

More than 500 Shiite Muslims were assembled for a traditional religious ceremony in the mosque when the suicide bomber struck. The death toll could have been much higher if the attacker had managed to enter the mosque, Nasir said.

"The suicide bomber was a young boy. When a security guard tried to check him with a metal detector, he blew himself up," said an eyewitness Waseem Ahmad.

The explosion also damaged half a dozen cars parked near the mosque gate.

"It was a horrible scene. The site was littered with human blood and flesh," a provincial lawmaker from Chakwal, Iffat Liaquat Ali said over phone after visiting the site.

Pakistan has a long history of sectarian attacks mostly against Shiite Muslims by Sunni extremist groups, which have joined hands with Taliban and al-Qaeda militants based in country's lawless tribal region near Afghan border.

The Chakwal attack is believed to be a part of what is being described by officials as a new wave of attacks by Taliban, who have threatened to step up strikes inside Pakistan till the government stops the US from carrying out drone attacks in tribal belt.

The Taliban accuse Islamabad, a key US ally in the international fight against terrorism, of providing assistance to US forces for these airstrikes.

On Sunday, a suicide bomber targeted paramilitary troops deployed in Islamabad's upmarket neighbourhood F-7/3 where several embassies, UN offices and residences of foreign diplomats are located. Eight soldiers and a civilian died and 12 others were injured.

Prime Minister Yousuf Raza Gilani condemned the attack as "deplorable act."

"It seems to be masterminded by people who are against the state and want to bring a bad name to the religion that has always called for tolerance and peace," he told reporters.

Gilani called upon media, civil society and all political parties to help in stamping out the menace of terrorism. dpa