Philip Hammond, British foreign secretary, has said that Russia could once again pose the greatest threat to Britain's security.
Speaking in London on Tuesday, he said the country's spy agencies were stepping up efforts to counter this.
"We are in familiar territory for anyone over the age of about 50 with Russia's aggressive behaviour a stark reminder it has the potential to pose the single greatest threat to our security," Hammond said.
"Hence continuing to gather intelligence on Russia capabilities and intentions will remain a vital part of our intelligence effort for the foreseeable future. It is no coincidence that all of our agencies are recruiting Russian speakers again."
Al Jazeera's Laurence Lee, reporting from London, said Hammond's "apocalyptic" tone was partly influenced by the fact that he, as a former defence secretary, was seeking more funding for the defence department from the country's coffers before the budget review next week.
"There are warnings of enormous cuts to Britain's military spending [and] 30,000 more military staff may lose their jobs," he said.
"It seems Hammond is making a stump speech for more funding from the government for his departments and using the threats of Russia and the Islamic State of Iraq and the Levant to justify that."
"No doubt that Hammond means it when he warns of the threats, but there is also internal politics at play as well."
For its part, Russia's Defence Ministry has confirmed the start of military exercises in the south of the country.
The exercises were launched in the region of Stavropol, reportedly involving artillery and multiple-launch rocket systems.
Source: Al Jazeera and agencies