Sir Michael Fallon said the initiative would continue for at least another year as the conflict in eastern Ukraine shows no sign of ending.
“Britain is stepping up in Europe and around the world,” the Defence Secretary said.
“Extending British training of Ukrainian Armed Forces sends a clear message that we support Ukraine and remain firmly committed to its sovereignty, independence and territorial integrity, in the face of a more belligerent Russia.”
Sir Michael said thousands of service personnel would be trained by British troops, who have been spread across around 14 sites across Ukraine since 2015
Around 100 training team members are active in the country at any one time, running 30 courses for infantry, medical and logistics corps, as well as on IED clearance.
British forces have already trained more than 5,000 Ukrainian troops, the Ministry of Defence said, saying they would remain until early 2018 at least.
The UK coordinates with four other nations in the “Quint” group, including the US, Canada, Lithuania and Poland.
The Government has also loaned a senior adviser to the Ukrainian government’s defence ministry and sent more than £1m of non-lethal equipment, including first aid kits and cold weather clothing.
Its latest deployment comes amid heightened tensions with Russia over Britain’s opposition to Vladimir Putin’s support for Bashar al-Assad in the Syrian civil war.
Diplomatic relations have worsened over the regime’s advance on Aleppo, with Theresa May saying civilians’ lives were in “President Putin’s hands”.
The Kremlin has hit back by denying all allegations of war crimes and claiming civilians were being held hostage by “terrorists”.
EU leaders also voted this week to extend economic sanctions against Russia over the Ukraine crisis after attempts at implementing a peace deal agreed in Minsk failed.
Successive rounds of EU and US sanctions have been imposed on Russia over the conflict and its annexation of the Crimean Peninsula in March 2014, prompting Russia to respond with counter-sanctions.
The Russian government has denied supporting pro-Russian separatist rebels in the face of evidence by Nato and monitors claiming to show its troops and weapons in rebel-controlled areas of the country.
Hacked emails seen by the BBC appear to show Vladislav Surkov, one of Vladimir Putin’s closest aides, detailing budgets for pro-Russian “republics” in eastern Ukraine, as well as a plan for Moscow to provide fuel for the separatists during shortages.
International investigators also concluded that rebels shot down a Malaysia Airlines passenger plane using a missile system supplied from Russia, killing all 298 people on board.
Rising tensions between Russia and Nato have sparked a military build-up on both sides, with Nato launching huge war exercises and making high profile deployments as Russia moves nuclear missiles nearer to European borders.
Mr Putin said the move was necessary to combat Nato “threats”, while military commanders vowed to continue developing Russia’s military capability.
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