A delegation from Japan's ruling Liberal Democratic Party is to visit beef production facilities in the US following allegations from opposition MPs that some US producers were failing to carry out thorough inspections on shipments to Japan.

US beef exports to Japan were suspended last month after backbones were discovered in a shipment of veal. Spines are considered to risk exposure to BSE and are prohibited under the terms of a deal which reopened the Japanese market to US beef producers in December.

Japan's opposition Democratic Party, critical of the government's failure to inspect plants before resuming imports in December, sent a delegation to the US to inspect facilities, and alleged that a beef facility operated by Kansas-based Tyson Foods Inc. did not completely remove all prohibited parts of cattle being processed. The Liberal Democrat group is also scheduled to visit a Tyson plant.

Tyson has denied the allegation, and the US Agriculture Secretary Mike Johanns has also spoken out against the opposition party's assertions.

The pro-US Liberal Democratic Party has also cast doubt over its rival party's findings.

"This is developing into a major diplomatic issue," said Tsutomu Takebe, secretary general of the Liberal Democratic Party. "They went with the intention of investigating how the problem occurred, but now the question is whether their inspections were conducted sincerely and fairly."