With the rapid pace of change in digital technology, we're constantly reviewing the processes and guidance our journalists use in their jobs.

As part of that, we have just distributed some refreshed breaking news guidance to our correspondents, reporters and producers.

It says that, when they have some breaking news, an exclusive or any kind of urgent update on a story, they must get written copy into our newsroom system as quickly as possible, so that it can be seen and shared by everyone - both the news desks which deploy our staff and resources (like TV trucks) as well as television, radio and online production teams.

So what about Twitter, the micro-blogging site where millions of people, including many of our journalists, communicate via short bursts of text?

We prize the increasing value of Twitter, and other social networks, to us (and our audiences) as a platform for our content, a newsgathering tool and a new way of engaging with people. Being quick off the mark with breaking news is essential to that mission.

We're fortunate to have a technology that allows our journalists to transmit text simultaneously to our newsroom systems and to their own Twitter accounts.

But we've been clear that our first priority remains ensuring that important information reaches BBC colleagues, and thus all our audiences, as quickly as possible - and certainly not after it reaches Twitter.

UPDATE 9 February 1330 GMT
To clarify any misconceptions, this guidance isn't about telling BBC journalists not to break stories on Twitter.

It's about making sure stories are broken as quickly and efficiently as possible to our large audiences on a wide range of platforms - Twitter, other social networks, our own website, continuous TV and radio news channels, TV and radio bulletins and programmes across several networks.

Equally that we can deploy the resources we need to tell that story on some of those platforms - reporters, TV trucks - as quickly and efficiently as possible.

We have a large, worldwide pool of correspondents, reporters and producers. So we're fortunate to have technology that allows them to get text into the BBC newsroom system and to their own Twitter accounts at the same time.

But when the technology isn't available, for whatever reason, we're asking them to prioritise telling the newsroom before sending their own tweet.

We're talking a difference of a few seconds. In some situations.

We absolutely understand the value of breaking news on Twitter, both in terms of our very successful branded activity like @BBCBreaking, and in terms of our individual journalists, who become sources of news for their followers. This guidance is absolutely compatible with that.

But it should be remembered that we are talking current guidance, not tablets of stone. This is a landscape that's moving incredibly quickly, inside and outside newsrooms, and the breaking news guidance - like our overall social media guidance - will evolve as quickly.

For those working for the BBC Persian service, interference and harassment from the Iranian authorities has become a challenging fact of life.

I am hugely proud of how they deal with that relentless pressure, and their unswerving commitment to delivering high quality, impartial journalism.

They arguably have the most difficult jobs in the BBC. They carry them out with unstinting dedication and in the knowledge that their work makes a critical difference to the lives of millions who crave access to free and accurate information, in a part of the world where it is scarce and extremely precious.

In recent months, we have witnessed increased levels of intimidation alongside disturbing new tactics. This includes an attempt to put pressure on those who work for BBC Persian outside Iran, by targeting family members who still live inside the country.

We remain extremely concerned about these actions by the Iranian authorities and the latest case only serves to underline this.

Last week the sister of a BBC Persian member of staff was arrested. She was detained and held in solitary confinement on unspecified charges at Evin Prison in Tehran. Although she has now been released on bail, her treatment was utterly deplorable and we condemn it in the strongest possible terms.

It is just the latest in a campaign of bullying and harrassment by the Iranian authorities, putting pressure on the BBC for the impartial and balanced coverage of events in Iran and the wider region.

It follows the repeated jamming of international TV stations such as BBC Persian TV, preventing the Iranian people from accessing a vital source of free information.

In recent months a number of relatives of members of BBC Persian staff have been detained for short periods of time by the Iranian authorities and urged to get their relatives in London to either stop working for the BBC, or to "co-operate" with Iranian intelligence officials.

In other instances, passports of family members have been confiscated, preventing them from leaving Iran. This has left many BBC Persian staff too afraid to return to the country, even to visit sick or elderly relatives. Some have had their Facebook and email accounts hacked.

In addition, there has been a consistent stream of false and slanderous accusations against BBC Persian staff in the official Iranian media, ranging from allegations of serious sexual assault, drug trafficking, and criminal financial behaviour.

It has also included claims that staff have converted from Islam to Christianity or Baha'ism - potentially a capital offence in Iran as it is considered to be apostasy. This has put our staff, who in most cases left their families behind to come to London and work for the BBC, under immense pressure.

This issue is wider than the BBC - other international media face similar challenges. But it is behaviour that all people who believe in free and independent media should be deeply concerned about.

The BBC calls on the Iranian government to repudiate the actions of its officials.

We also ask governments and international regulatory bodies to put maximum pressure on Iran to desist in this campaign of intimidation, persistent censorship and a disturbing abuse of power.

Mark Thompson is BBC director general.

As the number of people accessing BBC News via mobile phones and tablet devices continues to grow, I'm pleased to report that we have just launched a new version of the BBC News app specifically aimed at large Android tablets. (There's already an app for iPad and smaller 7 inch Android devices.)

In an average week, the BBC News site and apps are currently visited by about 9.7m users worldwide, or about 26% of the total. There are more details here from our Product Manager for mobiles, Kate Milner.

Steve Herrmann is editor of the BBC News website.