L'AQUILA, Italy, July 10 (Reuters) - Russian President Dmitry Medvedev warned the United States on Friday that if it did not reach agreement with Russia on plans for missile defence systems, Moscow would deploy rockets in an enclave near Poland.

In sharp contrast to his positive words during President Barack Obama's visit to Moscow earlier this week when the two reached broad agreement on nuclear arms cuts, Medvedev used a news conference at the G8 summit to return to Russia's earlier tough rhetoric on arms control.

Referring to an order he gave earlier this year to prepare deployment of short-range Russian missiles in the western enclave of Kaliningrad to answer to any U.S. deployment of a missile shield in central Europe, Medvedev said:

"If we don't manage to agree on the issues, you know the consequences. What I said during my state of the nation address has not been revoked."

Medvedev, speaking at the G8, also appeared to change his tone on the missile defence shield itself.

During Obama's visit he told the U.S. leader, using markedly softer language than normal, that "no one is saying that missile defence is harmful in itself or that it poses a threat to someone".

But in Italy on Friday, Medvedev returned to the Kremlin's traditional posture on the system, describing it as "harmful" and "threatening to Russia".

In Moscow, Medvedev and Obama agreed a target for cuts in nuclear arms and a year-end deadline for a reduction deal. Obama praised Medvedev as a "straightforward professional" leader. (Writing by Michael Stott; editing by Ralph Boulton)

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