Kabul (AFP) - Afghan authorities were warned about lax security at entrances to Kabul's highly fortified diplomatic zone before a suicide bomber struck this week, sources said Wednesday.
The attacker evaded the first security checkpoint on Street 14 in the heart of the capital on Tuesday before blowing himself up inside the "Green Zone", killing at least five people and wounding dozens.
It was the first attack targeting the heavily protected area that is home to many embassies and international organisations since a massive truck bomb detonated on May 31, killing or wounding hundreds.
Since then the Kabul government has ramped up security in the city, installing scanning machines, truck barriers and dozens of checkpoints to prevent militants reaching the diplomatic and downtown areas.
But Afghan authorities had been told that loose security checks at Street 14 posed a threat to those living and working inside the Green Zone, four Western and Afghan diplomatic and security sources told AFP.
Twice "we made it clear (to the National Security Council) that we have a problem with Street 14 -- there is no proper checkpoint because there is no barrier, just a bunch of policemen," a Western embassy official said.
He said another concern was the ability to avoid the first checkpoint by accessing Street 14 through a mosque and a park. The interior ministry said Wednesday that was apparently how the attacker got inside the Green Zone.
"It has been a group effort for a period of time (to warn Afghan authorities)," said a security expert working for a Western embassy, noting careless inspections of vehicles and pedestrians.
"That one (checkpoint) was a worry because it comes towards the British and Canadian embassies."
While security along the perimeter of the Green Zone has improved since the truck blast outside the German embassy five months ago, with more personnel stationed at checkpoints, it remained "porous", the expert said.
"This morning nothing had changed at this checkpoint -- they are sticking to the same procedure," another Western security source told AFP.
"This is like a huge highway in the middle of the Green Zone and besides that a big pedestrian way for all the people working there."
Defence ministry spokesman Dawlat Waziri defended the security arrangements, saying "many attacks are thwarted every day".
"Let's remember there are five or six million people living in Kabul and it is impossible to search everyone," he told reporters.
"This particular incident should also not be interpreted as negligence of Afghan security forces."
Attacks inside the Green Zone, which is heavily guarded and ringed by cement blast walls to protect against vehicle bombs, are extremely rare and Tuesday's assault has rattled some diplomats based in the area.
"It's definitely upsetting," a foreigner working for a Western embassy told AFP.
- Spate of assaults -
Taliban and Islamic State insurgents have launched a spate of suicide assaults on security installations and mosques in recent weeks, signalling their growing intention to strike even heavily defended targets.
"With attacks across the country almost daily and attacks in Kabul... the Taliban and IS are trying to demonstrate a lot of potency before the winter," Vanda Felbab-Brown, a senior fellow at the Brookings Institution, told AFP.
Last months police seized a lorry packed with 2,700 kilograms of explosives hidden under boxes of tomatoes in Kabul.
But security sources later told AFP the bomb-making material was only discovered because the driver had been involved in a traffic accident.
The penetration of the Green Zone was "highly problematic" and "a reminder of the profound security incapacities of the Afghan state", said analyst Michael Kugelman of the Wilson Center in Washington.
"We check a big number of trucks everyday. We first do a physical check, then sniffer dogs check them and then the trucks go through scanners," said Mohammad Yasin, a policeman at one of the newly established checkpoints near the airport, on a road leading to the diplomatic area.
"The trucks also should have a permission. We are working 24 hours a day with our foreign partners to protect the Green Zone," he said.
But another policeman working at a truck scanning site admitted it was impossible to check every vehicle coming in.
"Kabul has more than a hundred ways to enter the city," he said.