The chief of European police intelligence agency Europol is the latest law enforcement officer to raise concerns about encrypted communication services online.
Encryption has become one of the biggest problems for police and security services in dealing with threats from terrorism, Europol director Rob Wainwright told the BBC.
He warned that encrypted communcations make it difficult to monitor terror suspects, echoing comments in recent months by FBI director James Comey, former European Cyber Crime Centre head Troels Oerting and GCHQ director Robert Hannigan.
They have all said that the only way to meet this challenge is coming up with better arrangements for facilitating lawful investigation by security and law enforcement agencies.
They have also called for co-operation from US technology firms that are increasingly offering encrypted communication services in the wake of Edward Snowden’s revelations of National Security Agency internet surveillance.
Wainwright said he is concerned that technology firms are providing services for customers to encrypt data on their smartphones and develop instant messaging apps.
"We are disappointed by the position taken by these tech firms and it only adds to our problems in getting to the communications of the most dangerous people that are abusing the internet,” he said.
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However, TechUK, the UK's technology trade association, believes that national security and economic security security can be achieved with the right resources, co-operation between the security agencies and technology companies, and a clear legal framework for that co-operation.
TechUK underlined the need to resolve the tension between privacy and national security because the security of digital communications underpins the UK economy.
"Encryption is an essential component of the modern world and ensures the UK retains its position as one of the world's leading economies,” a TechUK spokesman told the BBC.
He said tech companies take their security responsibilities seriously and do engage with law enforcement and security agencies in the course of counter-terrorism and other investigations.
But, like many of his peers, Wainwright said current laws are "deficient" and should be reviewed to ensure security agencies are able to monitor all areas of the online world.
"There is a significant capability gap that has to change if we're serious about ensuring the internet isn't abused and effectively enhancing the terrorist threat,” he said.
Wainwright called for co-operation of legislators and technology firms in finding the right balance between privacy and security.
In November 2014, GCHQ director Robert Hannigan made a similar appeal, saying UK security agencies need support from large US tech firms in light of the fact extremist groups in Syria and Iraq have embraced the web.
“The challenge to governments and their intelligence agencies is huge – and it can only be met with greater co-operation from technology companies,” he said.
Earlier in March 2015, parliament’s Intelligence and Security Committee presented the prime minister with a set of proposals for the reform of privacy and intelligence laws.
The committee, headed by former foreign secretary Malcolm Rifkind, wants to amend, rewrite or redraft seven key laws governing the intelligence services and their activities.