The Scottish Parliament has suspended a debate on whether to call for an independence referendum following an attack outside the UK Parliament.
Presiding Officer Ken Macintosh said the incident in London was affecting the contributions of MSPs, and that the debate would resume at another time.
Four people – including an armed police officer, a woman and a man thought to be the attacker – have died.
Scotland Yard is treating it as a terrorist incident.
The woman was among several pedestrians struck by a car on Westminster bridge, before it crashed into railings.
The officer was stabbed in the Houses of Parliament by an attacker, who was shot by police.
Police said 20 people have been injured, including three other officers, and a “full counter-terrorism inquiry” is under way.
News of the London attack broke as MSPs were spending a second day debating whether or not to seek permission from the UK government for a second referendum on Scottish independence.
A vote had been due to be held at 17:30, but politicians including Scottish Conservative leader Ruth Davidson called for the session to be suspended.
Parliament officials initially ruled that the debate should continue as planned, before Mr Macintosh decided that it should be halted.
The presiding officer said: “The fact that our sister parliament has had a serious incident is affecting this particular debate, and is affecting the contribution of members. And so it is for that reason we are deciding to suspend the sitting.
“We will resume this debate and we will be able to do so in a full and frank manner, but I think to continue at the moment would not allow members to make their contributions in the manner they wish to.”
A decision on when the debate will resume is expected to be made on Thursday morning.
- Eyewitness accounts
- How the news broke
- Video: Aftermath on the bridge
- ‘Terror incident’: In pictures
Conservative MSP Fin Carson tweeted ahead of the presiding officer’s ruling that he had left the parliament chamber, saying: “I can’t understand how this debate can go on. At least a suspension would have shown some respect.”
However, some politicians were unhappy about the decision to suspend the debate.
Liberal Democrat MSP Mike Rumbles was among those to argue it was a “mistake”, telling BBC Scotland that had huge sympathy for those affected by the attack, but that: “We should not be giving in to terrorism, and I believe we’ve done that”.
Environment Secretary Roseanna Cunningham was also unhappy with the decision – but was later said to agree entirely after learning the full details of the London attack.
First Minister Nicola Sturgeon had been expected to win the backing of a majority of MSPs for her plan to ask the UK government for a section 30 order, which would be needed to hold a legally-binding referendum on independence.
The UK government has already said it will block the move, and will not enter into any negotiations until after the Brexit process has been completed.
Ms Sturgeon tweeted: “My thoughts are with everyone in and around Westminster caught up in this dreadful incident – and with the brave emergency services.”
She later said Scottish ministers had been liaising with Police Scotland, with officials holding a Scottish government resilience (SGoRR) meeting with the force “to ensure that any potential implications for Scotland are considered”.
A further SGoRR meeting was due to take place later on Wednesday evening.
The first minister added that she fully supported the suspension of the debate, but stressed the decision “was not because of any specific threat to the parliament or to Scotland”.
An email to MSPs, staff and Holyrood pass-holders from the Scottish Parliament chief executive’s office said: “While there is no intelligence to suggest there is a specific threat to Scotland, Edinburgh or Holyrood, we have increased security with immediate effect at the Scottish Parliament as a precaution.”
Police vehicles were seen outside the parliament building, with a spokesman for Police Scotland saying the force was “liaising with colleagues in London and will ensure appropriate safety and security plans are in place based upon what we know”.
Holyrood referendum debate halted after Westminster shooting}