Five men have been arrested in Cardiff and Barry on suspicion of terror offences, South Wales Police said.
It follows the arrests of two people in south-east London by Scotland Yard counter-terrorism police this morning.
South Wales Police said the group of five were arrested in relation to the support of banned organisations.
South Wales Police Assistant Chief Constable Nikki Holland said: "South Wales Police is proud to have strong links with our local communities and their co-operation is vital to make sure that we tackle radicalisation and extremism effectively together.
"I recognise the recent media coverage has raised very real concerns but I would like to thank and reassure the public that the links we have with our various religious communities remain strong and constructive.
"Following on from Counter Terrorism Awareness Week last week, which encouraged the public and businesses to be vigilant, I would like to ask once again for your co-operation and ask that you contact us if you know or suspect something.
"We will deal with information passed to us carefully and respond sensitively and proportionately."
The arrests were carried out by the North East counter terrorism unit assisted by the Wales extremism and counter terrorism unit.
During dawn raids in London a 33-year-old man was arrested on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism contrary to section 41 of the Terrorism Act 2000.
A 40-year-old man was arrested on suspicion of conspiracy to possess and supply fraudulent documents.
Both men remain in custody at a central London police station. Searches are taking place at four residential addresses in south-east London and one in Stoke.
The arrests are linked to five terror suspects who Metropolitan Police were given more time to question on Tuesday.
Two men, aged 33 and 43, were arrested in Dover on Sunday night by Scotland Yard anti-terror officers with armed support officers and Kent Police.
A 28-year-old man was arrested at the same port on Monday morning.
Under the same operation, two men, aged 24 and 40, were arrested on Monday in east London.
All five are being held on suspicion of being concerned in the commission, preparation or instigation of acts of terrorism.
The terror threat level in the UK was raised from substantial to severe a few months ago against a backdrop of increasing concerns over hundreds of aspiring British jihadis travelling to Iraq and Syria to learn terrorist ''tradecraft''.
Britain's chief counter-terror police officer, Mark Rowley, has warned the threat to the UK from jihadists will remain for ''several years''.
Fears of a terrorist attack on Britain's streets have heightened during the rise of Islamic State (IS), the extremist group that has taken over large swathes of Iraq and Syria and attracted thousands of foreign jihadists to its cause, including more than 500 Britons.
Last week, a new Counter-terrorism and Security Bill was introduced to Parliament, containing a range of powers including new orders that can block suspected British fighters from returning to the UK.
Ms Holland said counter terrorism should be viewed as a UK-wide problem, refuting suggestions the Welsh capital was a haven for extremists.
She told reporters: "The scale of counter terrorism in Wales is minimal compared to other parts of the UK.
"The difficulty in Wales is that we had the video in June and these three men, the Muthana brothers, have become poster boys in the UK. We're talking about three men compared to 550 plus who are out there fighting for Isil."