HARARE, Zimbabwe (CNN) -- Zimbabwean government forces began cracking down on the main opposition party Thursday, raising fears of a political crisis, according to witnesses and an opposition spokesman.

The forces raided at least two hotels in the capital, including one that houses foreign journalists, a witness said.

Four journalists were taken away about 8:30 p.m. (2:30 p.m. ET), he said. He said other journalists staying at the hotel were out on assignment, and he thought police might check their credentials when they returned.

The Zimbabwean government has denied CNN and other international news organizations permission to enter the country to report on the elections.

New York Times Executive Editor Bill Keller confirmed that Barry Bearak, a Pulitzer Prize-winning correspondent based in Johannesburg, South Africa, was taken into custody.

"He was apparently one of a number of Americans and other foreign nationals rounded up today," Keller said. "An American consular official who visited him at the central police station reported that he was being held for 'violation of the journalism laws.

"We are making every effort to assure that he is well treated, and to secure his prompt release," Keller said.

The identities of the other journalists seized in the raid were not immediately known.

State Department spokesman Tom Casey said the United States is calling for the immediate release of Americans seized by Zimbabwe authorities.

"We are concerned about the taking into custody of several American citizens," Casey said. "There is no reason for that. We want to see them released as soon as possible."

State Department officials said they were bound by privacy constraints and couldn't say how many American reporters were taken.

Adrienne Arsenault, an accredited journalist with Canadian Broadcasting Corporation, told CBC News that she was "surrounded and arrested" by Zimbabwe police. She said she was questioned and released within an hour.

"But the message was clear," said Arsenault, who was not one of the four taken into custody. "We are not wanted here, especially now."

Canada's Minister of Foreign Affairs, Maxime Bernier, called on Zimbabwe's government to allow journalists to freely cover the election.

"Canada is a strong proponent of the right to freedom of expression, including free media," Bernier said in a statement. "This applies equally to Zimbabwean and international media present in the country."

Tendai Biti, secretary-general for the opposition Movement for Democratic Change, said his party's offices -- in another Harare hotel -- were also raided by Zimbabwean forces.

Some of the rooms were ransacked, The Associated Press reported.

"There's a definite crackdown," Biti said. No one was detained in that raid, he added.

The action targeted "certain people ... including myself," Biti told the AP.

"It is quite clear he has unleashed a war," he said, referring to Zimbabwean President Robert Mugabe.

The crackdown came hours after the government announced another delay in releasing some of last weekend's election results, raising fears that Mugabe is trying to come up with a plan to remain in power. Many are predicting a runoff election. Watch why a runoff is likely »

In spite of this, on Wednesday the MDC declared Tsvangirai the outright winner, saying he took 50.3 percent of the almost 2.4 million votes.

The state-run newspaper The Herald reported Wednesday that Mugabe and Tsvangirai will compete in a presidential runoff because neither candidate garnered more than 50 percent of the vote. Watch the claims and counterclaims »

But even some in Mugabe's own party believe that he should step down. A Zanu-PF member, who did not want to be named for security reasons, reported a deep schism in the party Thursday,.

"The top guys have been given a rude awakening," the lawmaker said, adding that the party's brass is "shell-shocked" by the results and had not expected the apparent defeat.

The lawmaker, who lost his seat to an opposition challenger, said a presidential runoff "will be a suicide mission" and should be a "last resort" for the ruling party.

"Mugabe is finished," he added.

But Zimbabwean Deputy Information Minister Bright Matonga said he did not expect Mugabe to step down.

"I don't see that at all," he said. "And why should he? We have to go all the way. That is what the law says."

According to The Herald, the elections for parliament's lower house came down to a "photo finish," with MDC taking 99 seats and Zanu-PF 97.

Eleven posts in the 210-seat body went to an independent and members of a smaller opposition party. Three seats will have to be decided in a later election because the opposition candidates have died, the paper reported.

The Zimbabwe Electoral Commission said Thursday that it has postponed releasing results from elections for the Senate, parliament's upper house.

The government blames the delays in announcing results on logistics, noting that four elections were held simultaneously. Matonga has said the law gives the government until Friday to release the results. A look at the candidates »

Mugabe, who was prime minister before taking the presidential post in 1987, has been in power since Zimbabwe's independence from Britain 28 years ago. The election represents the toughest challenge to power he has ever faced. See photos from the country's elections »

A year after the last presidential election, which the MDC alleges was stolen, the government charged Tsvangirai with treason. He was acquitted. The MDC accused Mugabe of trying to eliminate him as a challenger.

Zimbabwe faced international sanctions after the 2002 election, including travel restrictions on Zimbabwean officials.

A hero of the country's civil war against the white Rhodesian government, Mugabe became the country's first black leader in 1980. Nearly three decades later, he has consolidated his rule over all aspects of Zimbabwean life.

Once revered for providing some of the best education and health care in Africa, Zimbabwe now has one of the lowest life expectancies in the world. Schooling is a luxury. It was once known as the breadbasket of southern Africa, but now it is difficult to get basic food supplies. Inflation has skyrocketed to more than 100,000 percent, while food production and agricultural exports have dropped drastically. E-mail to a friend

Journalist Eunice Mafundikwa in Atlanta, Georgia, contributed to this report.

All About Zimbabwe • Robert Mugabe • Morgan Tsvangirai