David Cameron has expressed “grave concerns” at reports that Russian military vehicles may have crossed into Ukraine and urged Moscow to find a peaceful resolution to the conflict.
In a telephone call with Ukrainian president Petro Poroshenko, the Prime Minister also warned a controversial aid convoy sent to the region by Russia must not be used “as a pretext for further provocation”.
Russia has denied that its troops entered its neighbour’s territory, insisting a convoy including armoured personnel carriers reported to have crossed the frontier were border guards who remained at all times on home soil.
Following the call, a Downing Street spokeswoman said: “They discussed the Russian humanitarian convoy on the Ukrainian border and the Prime Minister expressed grave concerns at reports of Russian military vehicles crossing the border.
“They agreed that humanitarian aid does need to reach those in the East but this should be delivered through the International Committee of the Red Cross.
“Russia should be co-operating fully with the ICRC and must not use the aid convoy as a pretext for further provocation.
“Both leaders also agreed on finding a political solution to de-escalate the situation and the Prime Minister welcomed President Poroshenko’s readiness to engage with Russia and other partners to achieve this. Russia needs to demonstrate the same willingness to find a peaceful resolution to the conflict.”
The UK has mad e £1 million available to support the humanitarian work, Mr Cameron told the president.
Ukrainian officials were earlier allowed to inspect the aid convoy, which Russia despatched for distribution around the rebel-held city of Luhansk.
Foreign Secretary Philip Hammond said the situation was “potentially very dangerous” as he arrived to discuss the situation with fellow EU foreign ministers.
Tensions between the West and Russian president Vladimir Putin have escalated following the apparent shooting down of Malaysia Airlines flight MH17 by Moscow-backed separatists.
After the meeting, EU foreign ministers urged Russia “t o put an immediate stop to any form of border hostilities, in particular to the flow of arms, military advisers and armed personnel into the conflict region, and to withdraw its forces from the border”.
They said they remained ” ready to consider further steps” in addition to the already-imposed sanctions on Russia and urged other countries not to seek to exploit a Moscow-imposed ban on some European food imports.
The Russian ambassador, Alexander Vladimirovich Yakovenko, was earlier summoned to the Foreign Office to account for the reports to a senior UK official.
“If true, such an incursion would be an unacceptable violation of international law and of Ukraine’s territorial sovereignty,” an FCO spokesman said.
Shadow foreign secretary Douglas Alexander said: “The Government is right to summon the Russian ambassador to explain reports that Russian military units have crossed into Ukraine overnight.
“If proved accurate, this is a provocative and aggressive attempt by Russian forces to undermine Ukraine’s security and its territorial integrity.
“Russia must end its military support for armed separatists in eastern Ukraine and should work to reduce tensions in the region, not inflame them.
“The Ukraine crisis represents not just a threat to European security but a significant geopolitical moment and, together, Europe must work harder to better influence critical calculations now being made in the Kremlin.”