Prime Minister David Cameron announced last month that Britain would send military advisers to Ukraine and provide an additional 15 million pounds ($22.3 million) in humanitarian aid.
An uneasy truce has been in place since last month between the Ukrainian forces and pro-Russian separatists in Ukraine's eastern Donetsk and Luhansk regions.
Last month, UK Defence Secretary Michael Fallon told Parliament that Britain was "providing additional nonlethal support" in the form of advisory and training teams.
"This support, provided at the request of the Ukrainian government, will help their armed forces develop and maintain the capacity and resilience they need, and help reduce fatalities and casualties," Fallon said.
The Organization for Security and Co-operation in Europe, which has been monitoring the ceasefire, said Wednesday that its observers had witnessed continued fighting in areas around Donetsk airport and Shyrokyne, east of the port city of Mariupol.
Kremlin spokesman Dmitry Peskov said the presence of foreign military instructors in Ukraine did nothing to reduce tensions, Russian state news agency Sputnik reported.
"Obviously, this is not helping in the building of trust or in easing the tensions in the conflict. It can be simply said that this is not aiding in the settlement, that's a fact," Peskov is quoted as saying.
The United States has promised to support an upcoming training program for Ukraine's National Guard forces.
Russia is under continued pressure from the West to end its support for the separatists. Moscow denies claims by Kiev and the West that it has trained and equipped the rebels, as well as sending Russian troops to fight alongside them.
Moscow signs South Ossetia treaty
In what Kremlin observers may see as another sign of defiance, Russia signed a treaty Wednesday with Georgia's breakaway territory of South Ossetia.
Russia sent its tanks into Georgia in 2008 and subsequently encouraged separatists
in its South Ossetia and Abkhazia regions to declare independence from Tbilisi.
NATO Secretary General Jens Stoltenberg condemned the "so-called treaty on alliance and integration" in a statement Wednesday, and repeated NATO's call for Russia to reverse its recognition of the territories as independent states and to withdraw its forces from Georgian soil.
"This so-called treaty is yet another move by the Russian Federation that hampers ongoing efforts by the international community to strengthen security and stability in the region," he said.
"It violates Georgia's sovereignty and territorial integrity, and blatantly contradicts the principles of international law, OSCE principles and Russia's international commitments.
"It does not contribute to a peaceful and lasting settlement of the situation in Georgia."