Britain is to send 10 armoured vehicles to bolster the international monitoring mission in eastern Ukraine amid renewed tensions between the pro-Russia separatist rebels in the government in Kiev.
Foreign Secretary Philip Hammond said the vehicles - worth £1.2 million together with associated communications equipment - would enable the monitors from the Organisation for Security and Cooperation in Europe (OSCE) to operate safely in the more volatile parts of the country.
At the same time Britain is expanding its contribution to the OSCE mission staff, with eight additional monitors arriving last week, and three more due to join them at the end of the month.
It follows an appeal from the current OSCE chairman-in-office, Swiss Federal President Didier Burkhalter, to member states for additional support.
The OSCE is responsible for monitoring and verifying a ceasefire agreed between the warring parties in Minsk in September.
There have since been numerous violations - leading to fears that the truce could unravel completely.
Mr Hammond said: "The UK stands squarely behind the Ukrainian people and government as they defend their nation's independence and work to make the political, economic and governance reforms that are vital to rebuilding the country.
"The OSCE will play a vital role in implementing the Minsk Protocol between Russia and Ukraine."