ISLAMABAD, Pakistan – After keeping quiet for much of the year as Pakistani President Pervez Musharraf suppressed domestic opposition, the United States on Monday issued an unusually harsh rebuke to the government for locking up key political rivals ahead of next week’s election.

“The reports of arrests of the leadership of several major Pakistani political parties are extremely disturbing and confusing for the friends of Pakistan,” said the statement issued by the U.S. Embassy here. “We wish to express our serious concern about these developments. These detainees should be released as soon as possible.”

Tasneem Aslam, spokeswoman for Pakistan’s Foreign Ministry, responded that the United States should stay out of the matter. “If the U.S. Embassy is confused, it would be well advised not to make such statements,” she said.

The embassy’s rebuke, coming just 12 days before elections in which Musharraf is expected to win a new term, appeared to mark a shift for the United States. American officials have largely refrained from criticizing the general, typically saying that his political maneuvering is an internal matter.

Musharraf, who came to power in a military coup eight years ago, is considered a key U.S. ally in counter-terrorism efforts, and Washington has been a staunch supporter even as his backing in Pakistan has plummeted.

In recent days, the government has rounded up opposition activists, including several members of parliament, and ordered them held for 30 days. Ameer ul-Azeem, spokesman for an anti-Musharraf religious party, said Monday that more than 500 people had been taken into custody overall, though the government said the number was far lower.

Musharraf’s candidacy for another term is being challenged at the Supreme Court by opponents who say they do not believe he can run because he remains an army general. The court is expected to rule within days.