The United States has joined human rights advocates in criticizing changes to Zimbabwe's constitution approved by the parliament in Harare Tuesday. The revisions are widely seen as entrenching the rule of President Robert Mugabe and his ZANU-PF party.

The State Department says it is troubled by the substance of the constitutional changes as well as the way they were pushed through the parliament, and sees them, overall, as a step backward for freedom in Zimbabwe.

Mr. Mugabe's ZANU-PF party, making use of the two-thirds majority it achieved in disputed March elections, approved the set of amendments on Tuesday.

Among other things, the amendments effectively bar white farmers from using the courts to challenge the seizure of their farms, under Mr. Mugabe's controversial land reform program.

They also give Harare authorities new ways to crack down on dissent, allowing it to seize the passports of Zimbabweans who have called for sanctions or military action against the Mugabe government.

The amendments drew sharp criticism from Zimbabwean human rights activists and the opposition Movement for Democratic Change, which said the revised constitution represents a serious assault on citizens' basic rights and freedoms.

The reaction from the Bush administration, which has been a persistent critic of the Mugabe government was similar. State Department Spokesman Sean McCormack expressed concern about both the changes and the amendment process.

"Some of the changes, as well as the process used to implement these changes in the constitution, are troubling," he said. "Overall, without cataloguing all of these, let me say that it's a sad step backwards for personal freedom, as well as the rule of law."

The amendments also include a provision setting up a second legislative chamber, the Senate, which critics say will be packed with Mr. Mugabe's allies.

The ruling party contends the changes will enable the government to conclude the redistribution of land to the country's black majority, and strengthen parliamentary democracy.

The United States has also been sharply critical, along with several other countries, of the slum-clearance program in Harare and other cities launched by the Mugabe government in May.

Several hundred thousand people were left homeless by the forced evictions and demolitions, carried out with the stated aim of cleaning up blighted city areas and removing illegal markets.

A United Nations report in late July demanded an end to the program, which it said has created an immense humanitarian crisis.

Australian Foreign Minister Alexander Downer said this week his government and New Zealand will press the United Nations to refer Mr. Mugabe for possible prosecution for crimes against humanity.

Mr. Downer said he had begun to discuss the idea of an International Criminal Court indictment of the Zimbabwean leader with U.N. Security Council members including Britain, though acknowledging the process would be difficult.

Mr. Mugabe, in power since 1980, has often accused domestic opponents of conspiring with his international critics, and suggested his government may be a target for "regime change" by foreign powers.