Media playback is unsupported on your device Media caption Philip Hammond: "A huge burden of responsibility also lies with those who act as apologists"

"Apologists" for those who commit acts of terrorism are partly responsible for the violence, Philip Hammond has said.

Security services have been criticised over their handling of Mohammed Emwazi - known as "Jihadi John".

But in a speech the foreign secretary praised the "brilliance" of Britain's intelligence officers.

Mr Hammond also warned of Russia's "aggressive behaviour", saying it could "pose the single greatest threat" to the UK's security.

Gathering intelligence on Russia's intentions would be a "vital part" of the work of Britain's intelligence agencies for the "foreseeable future", he added.

MI5 'harassment'

In another development due later, MPs are expected to approve new travel restrictions for people the government believes pose a "terrorism-related threat".

The motion will also introduce fines for airlines which breach a series of requirements set up to "prevent certain individuals from travelling to or from the UK".

In the speech at the Royal United Services Institute (Rusi) in London, Mr Hammond said ministers must act "decisively" in debates about powers given to the security services so they can "get on" with keeping the UK safe.

He said: "The exposure of the alleged identity of one of the most murderous Isil (Islamic State or IS) terrorists over the last few weeks has seen some seeking to excuse the terrorists and point the finger of blame at the agencies themselves.

"We are absolutely clear; the responsibility for acts of terror rests with those who commit them.

"But a huge burden of responsibility also lies with those who act as apologists for them."

Cage, an advocacy group for those "impacted by the War on Terror", has said MI5 played a role in the radicalisation of the Kuwait-born Briton.

Its research director Asim Qureshi told the BBC "harassment" by intelligence officers did not make Emwazi into a killer, but he said it was a factor in making him feel he "didn't belong in the UK anymore".

Analysis

Image copyright AP Image caption GCHQ headquarters

Gordon Corera, BBC security correspondent

Britain's spies are today in the spotlight in a way they never were in the past - their powers and performance questioned.

But the politicians also say they are needed now more than ever, thanks to an uncertain world with a myriad of emerging threats.

This speech by the foreign secretary, the political master of GCHQ and MI6, was a robust defence of the spies' work against criticisms covering both recent revelations about Mohammed Emwazi, the man revealed to be IS fighter Jihadi John, and broader questions about security and privacy in the wake of the Edward Snowden disclosures.

But as well as the message that the spies needed to keep up with modern demands, whether the pace of technological change or for greater accountability from the public, there were also echoes of the past.

These were clearest when it came to Russia as Philip Hammond said it was no coincidence that all three UK intelligence agencies were again recruiting Russian speakers for their work.

Who is Mohammed Emwazi?

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Emwazi was born in Kuwait in 1988 and came to the UK at the age of six.

He went to school in London and graduated from the University of Westminster in 2009 with a degree in computing.

He came to the attention of security services in the same year and was deported as he tried to enter Tanzania, though the circumstances of this are disputed.

He then spent two spells in Kuwait, but Cage said he was prevented from returning to the country after a trip to Britain.

He later went missing, and police told his family he had gone to Syria.

He has subsequently been identified as the militant in the August 2014 video showing the murder of US journalist James Foley, and in several similar videos showing the beheading of hostages.

Read the full profile here.

'Unprecedented demand'

Mr Hammond said the recent case of the three teenage London schoolgirls believed to have travelled to Syria to join IS showed there were "things we can improve".

But he said it it was not just the security services but parents, schools and community workers who were responsible for preventing people from travelling to countries like Syria and becoming a security threat.

Britain needed to maintain a "highly effective, secret capability" to identify, monitor and act against terrorist threats, the foreign secretary said.

The number and range of cases amounted to the "greatest challenge to our collective security for decades and places unprecedented demands on those charged with keeping us safe," he said.

Russia 'threat'

In the past 12 months Parliament has passed two acts which included more powers for security services to access people's communications data.

In January David Cameron said he would give authorities "very intrusive" powers to close "safe spaces" used by suspected terrorists online if he won May's election.

Mr Hammond said the emergence of militant groups such as IS and Boko Haram show the "pace" with which threats to UK security are "evolving".

He also accused Russian President Vladimir Putin of "subverting" the system of rules which "keeps the peace between nations" by annexing Crimea and "now using Russian troops to destabilise eastern Ukraine".

He said Russia's actions, such as modernising its weapons and the "increasingly aggressive stance" of its military, were all "significant causes for concern".

Mr Hammond said: "We are in familiar territory for anyone over the age of about 50, with Russia's aggressive behaviour a stark reminder that it has the potential to pose the single greatest threat to our security."

Mr Hammond added it was "no coincidence" that all of the UK's security agencies were recruiting Russian speakers again.

Russia denies having troops in Ukraine, saying that any Russian soldiers among the rebels are "volunteers".