Britain criticised Wednesday a report by a UN human rights investigator on Israel's Gaza offensive as "unbalanced", but insisted it was extremely concerned by the situation in Gaza and the West Bank.

Last month, the UN special rapporteur on the Palestinian territories, Richard Falk, said in a report that there was "reason" to conclude that Israel's massive military offensive on Gaza in December and January was a war crime, but the Jewish state slammed the report as "one-sided".

"The report of the UN Human Rights Council's Special Rapporteur is unbalanced and contributes little," junior foreign minister Bill Rammell said in a written reply to a parliamentary question published Wednesday.

Rammell noted that Britain called for an immediate ceasefire throughout the Gaza conflict earlier this year, and said Britain was "extremely concerned with the current situation in occupied Palestinian territories."

He added: "We are awaiting the results of several ongoing investigations into alleged human rights violations during the Gaza conflict and will consider very carefully the results of these investigations once they are available.

"We continue to press the Israeli government to abide by all its international commitments, including its obligations under the fourth Geneva convention which makes clear that an occupying power must co-operate in allowing allow free movement of people, humanitarian supplies and commercial goods."

The 22-day war killed more than 1,300 Palestinians and 13 Israelis and left swathes of the impoverished Hamas-run territory in ruins.

Israel launched its war in retaliation for persistent rocket fire by militants in Gaza.

It ended after Hamas and Israeli each declared ceasefires on January 18 but sporadic violence has continued since and Egyptian-brokered efforts to forge a more sustainable truce have yet to succeed.