Brammertz said that last October Croatia created an inter-agency Task Force to take over the administrative investigation into those documents.

While his Office noted "a general improvement in the quality of Croatia's administrative investigation in terms of the manner in which interviews were conducted, the investigation falls short of providing a full account of the whereabouts of the requested documents. Key investigative avenues remain unexplored," he said.

Brammertz said that in the past several weeks he had been assured by Croatian authorities that the administrative investigation would be expanded, in line with activities suggested by his office one year ago. He was hopeful that those activities would result in effective action and concrete results.

Brammertz underlined that as long as this issue remained before the tribunal, he would wait for the results of Croatia's efforts to see if the country had intensified the administrative investigation into the missing documents and to fully account for them before the end of the trial in question.

Brammertz has been asking since 2008 that Croatia submit artillery logbooks from the 1995 Operation Storm as evidence in the trial of generals Ante Gotovina, Ivan Cermak and Mladen Markac.

The outstanding issue of those documents brings into question Croatia's "full cooperation" with the Hague tribunal, which is a condition for opening the policy chapter on the judiciary and fundamental rights in Croatia's accession negotiations with the European Union.

According to diplomatic sources, EU foreign ministers decided, based on talks with Brammertz in Luxembourg on June 14, to allow the opening of said policy chapter, leaving "full cooperation" with the tribunal as a condition for closing the chapter.

In a debate, the US representative to the Security Council, Brooke Anderson, praised Croatia's cooperation with the Hague tribunal and renewed commitment to credibly continue with the investigation and to find the artillery logbooks and, if it could not locate them, to carry the investigation through.

She said the US encouraged Croatian authorities to continue pursuing additional techniques of investigation that could help get those documents back.

The British Ambassador to the UN, Mark Lyall Grant, welcomed Brammertz's assessment that Croatia was generally responding to the needs of his office and that cooperation had progressed since his previous report.

Other Security Council members too welcomed Brammertz's report, calling on Croatia to continue searching for the missing documents.

Brammertz commended Serbia's cooperation with the Hague tribunal, underlining that over the past six months it promptly responded to the requests of the Prosecutor's Office and that currently there were no outstanding requests for assistance.

He underlined the importance of wartime diaries belonging to fugitive Ratko Mladic, which Serbian authorities seized in February and turned over to the tribunal, announcing they would be entered as evidence in several ongoing trials.

Brammertz underlined that the main priority of the Prosecutor's Office was the arrest of the last two fugitives, Mladic and Goran Hadzic.