MINSK, July 21 - Ukraine and pro-Russian separatists have reached a preliminary agreement to extend a pull-back of weapons in east Ukraine to include tanks and smaller weapons systems, the chairman of the OSCE security watchdog, Ivica Dacic, said on Tuesday, Reuters reported.

Under a ceasefire agreement brokered in Minsk, Belarus, in February, weapons of over 100 mm caliber are meant to have already been withdrawn, but both sides accuse the other of continuing to use heavy artillery and casualties are reported almost daily.

The latest agreement on lighter weapons was reached at a meeting of the so-called "contact group" involving Ukraine, Russia and the separatists under the auspices of the Organization for Security and Cooperation in Europe.

Speaking in Minsk, Dacic said the deal still needed to be signed, but urged all sides to "completely cease attacking and respect a full ceasefire.”

Ukrainian and U.S. troops launched drills Monday near the war-torn country's Polish border in a bid to show unity and resolve in the face of an increasingly defiant Kremlin.

The annual Rapid Trident exercises involve 1,800 soldiers from 18 countries and last for just under two weeks, AFP reported.

Their immediate aim is to build morale and cohesion within the ex-Soviet state's outdated and woefully underfunded armed forces -- caught in a 15-month east Ukrainian quagmire battling pro-Russia militias that has claimed more than 6,500 lives.

But they also deliver a transparent message to the Kremlin about Washington and its allies' determination to thwart any expansionist ambitions Russian President Vladimir Putin may have.

"These joint maneuvers... display a broad support for Ukraine in its struggle for freedom and sovereignty," Ukrainian forces commander Oleksandr Syvak told the festive flag-raising ceremony.

His US counterpart Alfred Renzi said the participating countries -- most of them NATO members but also including such former Soviet nations as Moldova and Azerbaijan -- "will prove an ability to cooperate as one unified force for stability."

Russia quickly condemned the war games as a threat to an already shaky five-month truce agreement that aims to resolve one of Europe's bloodiest conflicts in decades by the end of the year. (rt/ez)