Newspaper headlines: 'Johnson jets in to Iran crisis' and 'SAS to Iraq'

The Observer's front page has a picture of Iranian paramilitary forces, with their fists raised in the air, during an anti-American protest in Tehran on Saturday.

The march was in response to the killing of the country's most senior military commander, Qasem Soleimani. Under the headline "Doubts grow over US case for killing", the Observer suggests America's traditional allies are uncomfortable about Thursday's drone strike in Iraq.

It highlights the fact that President Emmanuel Macron of France telephoned Iraq's acting prime minister to express support for the country's sovereignty. The paper calls this an "implicit rebuke" of Washington's action.

"Brit nuke sub alert", says The Sun on Sunday, which reports a Royal Navy nuclear-powered submarine armed with Tomahawk cruise missiles is in position to strike Iran if tensions give way to war in the Middle East.

The paper's leader column urges Boris Johnson to - in its words - "make a strong stand against an Iranian regime, which has regularly threatened Britain".

The Sunday Telegraph suggests Britain should choose this moment to break away from European Union foreign policy on Iran.

It is critical of the EU's attempts to re-kindle the Iranian nuclear deal - arguing that Tehran has been "violating" it by investing in missile technologies that could deliver a nuclear attack.

The leader in the Mail on Sunday expresses major reservations about the killing of General Soleimani. It accepts that "there have been few more sinister figures in the Middle East".

But it goes on to say that "no amount of satisfaction at his departure can overcome the problem of how he died".

The headline "Keir we go" is how the Sunday Mirror reveals that the shadow Brexit Secretary, Sir Keir Starmer, has joined the race to succeed Jeremy Corbyn as Labour leader.

The Mirror says Sir Keir - who sets out his stall in the paper - is the favourite to secure the job, ahead of candidates including shadow foreign secretary Emily Thornberry, and the MPs Lisa Nandy and Clive Lewis.

The Sunday Times reports on how scientists plan to reduce the grey squirrel population across the UK by altering the animals' genes. Grey squirrels, which were imported from America, spread a virus which has caused a huge decline in the numbers of red squirrels, which are native to Britain.

The Times explains that researchers at the Roslin Institute - which created Dolly the cloned sheep in 1996 - have come up with a scheme that involves changing the grey squirrels' DNA, so that females born in the future will be infertile.

And the Sunday Express is one of several papers to preview tonight's Golden Globe awards in Los Angeles.

It says a number of Hollywood stars have asked not to have seats in the front row at the event - because they're worried that they might become the butt of jokes from the ceremony's host, Ricky Gervais.

The Express explains that the comedian has upset several stars during his time as host of the film and television awards - and now some celebrities want to avoid catching his eye.

The People carries the same story with the headline: "Tricky Ricky".