The escalating war of words over the poisoning of an ex-spy in England is just one of a slew of diplomatic rows clouding Russia's preparations as hosts of the World Cup this summer.

Sport's most-watched event is usually a prime opportunity to burnish the host country's international image -- but that will be tricky for Russia given its dismal relations with the West.

Here are five sources of international tension away from the pitch as Russia prepares for the FIFA tournament in June and July:

- Spy poisoning -

Western allies have lined up to back Britain over the nerve agent attack on a former Russian double agent in an English street, leaving Moscow increasingly isolated.

Both Britain and the United States have said the Russian state was likely responsible for the attempted assassination of Sergei Skripal, an accusation furiously denied by Moscow.

As calls mount in the British press for a World Cup boycott, Moscow has accused Britain of seeking to "undermine trust" in the hosts.

"How can we go to Putin's World Cup now?" read Tuesday's front page in the Daily Mail newspaper, which had earlier argued that taking part would hand Russia "a bloody stamp of approval".

The British government has so far threatened a boycott by officials and dignitaries, but there are as yet no plans to withdraw the England squad.

Simon Chadwick, who writes about sport and geopolitics at England's University of Salford, said Russia was more concerned about using the Cup to boost President Vladimir Putin's image at home than abroad.

"It's about projecting an image of Russia as strong and powerful," he said, just as the Kremlin used the 2014 Sochi Winter Olympics to build Russians' sense of their nation as a resurgent global power.

- Syria -

Russian support for Syria's President Bashar al-Assad has put the Kremlin at odds with the opposition-backing West since the brutal war broke out in 2011.

Russia provides air power and back-up for Assad's troops and has repeatedly blocked Western attempts at the United Nations to introduce ceasefires or launch investigations into alleged chemical weapons use.

Its peace talks known as the Astana process are also a rival to the UN-backed Geneva discussions.

Russia wants to be the key power broker in postwar Syria, said Mathieu Boulegue, Russia research fellow at the Chatham House think-tank.

"It's trying to increase its military footprint on the ground, it's trying to increase its economic footprint," said Boulegue -- developments that worry the West.

- Cyberattacks -

Since US accusations of Russian interference in the 2016 presidential election, various Western governments have warned against Russian attempts to meddle in their domestic affairs.

Reports of Russian "troll factories" spreading fake news online to influence voters have spread fears from the United States to France, Britain and Catalonia.

Moscow has repeatedly denied allegations of electoral interference, but analysts view its cyber-activities as part of long-term efforts to weaken the West.

"There is in Russia a systematic approach seeking to destabilise the West from within," said Boulegue.

- Ukraine -

Russia annexed the Crimea peninsula in 2014 after a pro-Europe popular uprising ousted Ukraine's Kremlin-backed president.

Since then, more than 10,000 people have been killed in the war in Ukraine's east between government forces and Russian-backed rebels.

Chadwick noted that the Crimean invasion came just after the Sochi Games, which at home became "almost a symbol of Russia's ascendancy to becoming a powerful global force again".

And while hosting the World Cup might win few friends abroad, Putin could use the football tournament to pull off a similar domestic public relations coup this summer, he predicted.

- Doping -

The World Cup comes after months of controversy over the doping of Russian sportsmen and women.

They were booted from the Olympics over allegations that Russia carried out state-sponsored doping at the 2014 Sochi Winter Games.

But a 168-member team of Russian athletes was allowed to take part in the just-completed Pyeongchang Winter Olympics under a neutral banner.

At those Games, "there were two or three Russian athletes who were banned, but essentially that passed off without any particular controversy when to came to Russia and doping," Chadwick said.

The International Olympic Committee lifted the ban against Russia last month on condition there be no further doping after Pyeonchang.

But further troubles could be on the horizon.

"Football seems to have had relatively little scrutiny in doping terms compared to athletics and swimming," he said.

"There has been speculation in the press for the best part of a year that football will be exposed to the same kind of scrutiny, and there may well be countries that come out badly."

Should a fresh doping scandal break during the World Cup, he predicted, it would be a major blow to "Putin's grand project" of pulling off the huge event smoothly while the world watches.