* Newspapers cite early intelligence warnings of mall attack
* Official says prior intel cannot always avert attacks
* Kenyan, foreign experts investigate wrecked mall building
* Identities, nationalities of attackers still not known
By Matthew Mpoke Bigg and James Macharia
NAIROBI, Sept 28 (Reuters) - Kenya is "at war" with Islamistmilitants who attacked a Nairobi shopping mall, the governmentsaid on Saturday as it faced questions about whether it hadreceived advance intelligence warnings of the deadly strike.
A week after the raid on the Westgate shopping centre thatkilled 67 civilians and police and was claimed by the Somalimilitant group al Shabaab, the government has been trying toreassure Kenyans that it can protect them from further attacks.
Three Kenyan newspapers reported on Saturday that a year agothe country's National Intelligence Service (NIS) had warned ofthe presence of suspected al Shabaab militants in Nairobi andthat they were planning to carry out "suicide attacks" on theWestgate mall and on a church in the city.
In front-page stories, the Nation, Standard and Starnewspapers questioned whether the Kenyan government and militarymay have failed to act on this and more recent warnings thisyear by local and foreign intelligence services.
"It is not a 'yes' or 'no' answer," Mutea Iringo, principalsecretary in the Ministry of Interior, told Reuters.
"Every day, we get intelligence and action is taken as perthat intelligence and many attacks averted. But the fact thatyou get the intelligence does not mean something cannot happen,"the senior official added.
"What we are saying is that we are at war, and that everyday some young Kenyan is being radicalised by al Shabaab to killKenyans," Iringo said, calling on citizens across the eastAfrican nation to be alert and cooperate with authorities.
The newspaper reports emerged ahead of a meeting on Mondayof the Kenyan parliament's defence and foreign relationscommittee which is expected to ask security chiefs how muchwarning they had of Saturday's assault.
In the mall attack that extended into a four-day siege,gunmen fired on shoppers and tossed grenades leaving a trail ofvictims and shocking Kenya and the world. Al Shabaab said itacted in revenge against Kenyan troops who have been fighting itin neighbouring Somalia for two years.
Britain's government said on Saturday a sixth Britishnational had been identified among those killed at the mall.French and Canadian nationals also died.
The Star quoted another NIS briefing in February warning ofa gun and grenade attack in Kenya similar to a three-day killingspree by militants in the Indian city of Mumbai in 2008.
In an editorial, the Standard said the reports pointed to"obvious" security lapses. "It is becoming increasingly apparentthat the country's top security organs may have receivedadequate briefing on imminent terror threats," it said.
"Why they did not act in time to save the needless deaths atWestgate is astonishing and dumbfounding," it added.
The possibility that al Shabaab, which has carried outprevious smaller gun and grenade attacks in Kenya, may beplanning further high-profile strikes presents a major securitychallenge for President Uhuru Kenyatta, elected in March.
But the incident has also rallied foreign support for him ashe confronts charges of crimes against humanity at theInternational Criminal Court in The Hague. He deines charges oforchestrating violence following Kenya's disputed 2007elections.
FORENSIC PROBE UNDER WAY
Five of the mall attackers were killed and Kenyanauthorities say they are holding eight people over the raid,which confirmed Western and regional fears about al Shabaab'sability to strike beyond Somalia's borders.
It also dented Kenya's vital tourism industry, although thefinance minister says it will not have a long-term impact.
Kenyan officials have not so far specified the identities ornationalities of the attackers, saying forensic investigation ofthe wrecked mall building and of the dead will take time.
This has produced a deluge of unconfirmed speculation thatradicalised diaspora Somalis from the United States and Europemay have been involved in the al Shabaab operation.
U.S., Israeli and European forensic experts are helpingKenya in the investigation.
A week after the attack, the five-storey, beige-colouredmall remained sealed off to the public. From outside, a spray ofbullet holes was visible around one upstairs window.
A team of foreign officials wearing white protectiveclothing and yellow boots could be seen leaving the mallescorted by an armed man wearing a black flak jacket.
Kenyan and Western officials have said they cannot confirm speculation that Briton Samantha Lewthwaite, widow of one of the2005 London suicide bombers, had a role in the mall attack. Somesurvivors said they saw an armed white woman.
Kenya requested a "red alert" wanted notice issued byInterpol for Lewthwaite, dubbed the "White Widow" by the Britishmedia, but said she was wanted in connection with a previous2011 plot that was also linked by police to al Shabaab.
With the country's security services on high alert, someKenyans said they were worried that the government may havefailed to act on prior intelligence information.
"It sounds like laxity. If you get warnings ... you have gotto listen to those warnings," said businessman Vipool Shah.
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