Security forces in Kenya are seeking to crack down on insecurity following the assassination of a Muslim cleric in Mombasa and a triple bombing in Nairobi earlier in the week.
Abubakar Shariff Ahmed, who was killed on Tuesday, was accused by the UN Security Council of recruiting young Kenyans for al-Shabab.
Kenya police said they have arrested more than 1,000 people in the Nairobi neighbourhood of Eastleigh, whcih has a large Somali population, after a triple bombing claimed six lives there on Monday.
About 400 of the suspects were held on Tuesday night as police set up roadblocks and went door to door searching for suspects.
Police said two of the detainees were in possession of grenades. The police also detonated an explosive device that was discovered in Eastleigh on Wednesday.
DW correspondent James Shimanyula says most of the recent attacks were blamed on Somalis who entered Kenya illegally.
Mombasa calm bit tense
Meanwhile heavily armed police patrolled the streets of the port city of Mombasa on Wednesday one day after a prominent radical Muslim cleric was assassinated.
The city, a key transport hub for East Africa and a popular tourist destination, was reported calm, with the slain cleric's Masjid Shuhadaa mosque broadcasting appeals for restraint among his supporters.
The deceased cleric, Abubaker Shariff Ahmed, was a vocal supporter of the late Osama bin Laden. He was on UN sanctions lists and was accused of being a "leading facilitator and recruiter of young Kenyan Muslims for violent militant activity in Somalia." He was also alleged to have "strong ties" with al-Shabab leaders.
Kenya contributes troops to the UN-mandated African Union force AMISOM, which has been battling al-Shabab militants in Somalia since 2007.
Terrorist incidents have risen in Kenya after a brief lull following the attack on the Westgate shopping mall in September 2013
Ahmed, better known as Makaburi or "grave" in Kiswahili, had described last year's attack on the Westgate shopping mall in Nairobi as "100 percent justified." Al-Shabab claimed responsibility for the raid in which at least 67 people died.
Clerics' deaths sparked riots
Ahmed's death was the latest to hit the Mombasa Masjid Shuhadaa mosque, which Kenyan officials call an incubator of terrorism. Sheik Aboud Rogo Mohammed, a friend of Ahmed's, was assassinated in August 2012. A year later another mosque leader was killed. There have been no arrests in either case.
Such killings have sparked deadly riots, with clerics' supporters clashing with the police. There were initial angry scenes outside the police station where Ahmed's body had been taken on Tuesday, and police fired into the air to push back furious supporters.
Ahmed, dressed in white robes, had been shot in the chest near Shimo la Tewa prison in Mombasa. Another man was killed with him. Senior police officer Richard Ngatia said there were three survivors of the attack, who didn't know who had shot at them. "We don't know who shot them or why," he said.
One of the survivors, a preacher named Mohamed Ali, told local media that the second man who had been shot and killed was Hafidh Bahero. Ali said police had ordered the survivors to "stay on the ground with their faces facing down and not to talk to one another." They were placed in the same vehicle as the two corpses and taken to Bamburi police station, he added.
Local media report that hundreds of mourners carried the biers bearing the two bodies and walked over two miles (three kilometers) to bury them.
Following the two earlier killings, Ahmed had told the AP news agency in October he believed he was marked for death. "The same guy who ordered Aboud Rogo's death is going to order mine," he said.
Interior Minister Jospeh Ole Lenku said Shariff's killers will be arrested like any other suspected terrorists.
Sheikh Muhdhar Khitamy, regional chairman of the Surepme Council of Kenya Muslims, said "we condemn this extrajudicial killing and we are far from happy with the security situation here - these killings have to stop."