Ukraine crisis: 'Rebel reinforcements' raise fears

(BBC) - The US and the European Union have expressed concern at reports of a build-up of separatist reinforcements in eastern Ukraine.

Shelling around the city of Donetsk on Sunday followed an intense overnight artillery bombardment, shaking an already fragile ceasefire.

Monitors and journalists reported unmarked convoys of heavy weapons, tanks and fighters close to the city.

Russia denies claims that it is supplying the separatist rebels.

The EU's head of foreign policy, Federica Mogherini, said the latest reports were "worrying".

"The most recent reports by the OSCE [Organisation for Security and Co-operation in Europe] Special Monitoring Mission in Ukraine about convoys in separatist held areas with substantial amounts of heavy weapons, tanks and troops without insignia moving westwards represent a very worrying development," she said.

The White House warned that any efforts by pro-Russian rebels to seize more territory would be a "blatant violation" of the ceasefire agreement signed in Minsk in September.

"We are very concerned by intensified fighting in eastern Ukraine, as well as numerous reports... that Russian backed and supplied separatists are moving large convoys of heavy weapons and tanks to the front lines of the conflict," said US National Security Council spokeswoman Bernadette Meehan.

"We continue to call on all sides to strictly adhere to the ceasefire. Any attempt by separatist forces to seize additional territory in eastern Ukraine would be a blatant violation of the Minsk agreements."

More than 4,000 people have died since fighting erupted in April after pro-Russian separatists seized control in the regions of Donetsk and Luhansk.