Four people were killed in a bomb blast in Pakistan's northwest on Friday and police foiled planned suicide attacks on the capital Islamabad and neighbouring Rawalpindi city.
A bomb exploded in a deserted area in the town of Dera Ismail Khan without causing damage. But as police and civilians gathered at the scene, another bomb exploded that killed four people, including two policemen.
Nine people were wounded in the blast, the town's police chief Mohsin Shah told Reuters. Dera Ismail Khan is close to South Waziristan tribal region, a known sanctuary for al Qaeda militants and their allies.
On Thursday, police arrested six people and seized three vehicles packed with explosives in Rawalpindi.
"We have arrested suspected suicide bombers," said Rao Iqbal, Rawalpindi police chief.
The arrests came after al Qaeda carried out a suicide car bomb attack on the Danish embassy in Islamabad on Monday that killed six people, all of them Pakistani.
The arrests triggered a high alert.
Security was tightest along Islamabad's Constitution Avenue, the dual carriageway leading to the presidency building, National Assembly, Supreme Court, several ministries and the diplomatic enclave where many embassies are located.
Concrete barriers were placed across the broad avenue, and regular entry points to the enclave were closed, while razor wire was laid around the perimeters of key buildings.
The Danish mission, under threat since the publication of cartoons of the Prophet Mohammed by Danish newspapers in 2005, was located in a plush residential neighbourhood.
A Danish team has arrived in Pakistan to work with Pakistani agents investigating the embassy attack.
A senior Pakistani official of the joint investigation team said several people had been detained, but none had been linked to the attack so far. Police were preparing a sketch of the suspected bomber.
Foreign envoys met on Thursday with Rehman Malik, the adviser to the prime minister on the interior, and he told them Islamabad police were being reinforced with paramilitary troops.
Malik assured those ambassadors whose embassies are outside the diplomatic enclave that he would take up issues regarding the provision of new sites for them to move to.
The Netherlands mission has moved to a hotel with tight security, having come under threat because of a film made by a Dutch anti-immigration politician that is deemed offensive to Muslims.