Malaysian Prime Minister Abdullah Ahmad Badawi, whose government arrested critics and a journalist on Friday, faces mounting pressure from an opposition alliance and dissent within his own party that could presage a challenge to his leadership.

A three-party opposition alliance led by Anwar Ibrahim has pledged to topple 68-year-old Mr. Abdullah. Mr. Anwar seeks to lure enough government members of parliament to his side to win a no-confidence vote against the ruling National Front coalition, which has been in power since Malaysia’s independence in 1957.

The opposition is expected to miss its initial target date of Sept. 16 to vote out Mr. Abdullah’s government. But Mr. Anwar said Sunday that his alliance already “has the numbers” to defeat the National Front. “My personal target is within September,” he said in a telephone interview.

At the same time, Mr. Abdullah has to deal with rising opposition within his own party, the United Malays National Organization. International Trade Minister Muhyiddin Yassin, an UMNO vice president, last week publicly questioned Mr. Abdullah’s plan to stay in office until mid-2010 before handing leadership to Deputy Prime Minister Najib Abdul Razak — hinting that the prime minister should step down sooner.

Mr. Muhyiddin also said 83-year-old former Prime Minister Mahathir Mohamad, a critic of Mr. Abdullah, is prepared to rejoin UMNO after resigning in May. Some political analysts speculate that the developments signal a move by party dissidents to push Mr. Abdullah from power at UMNO’s annual meeting in December, if not before.

“Abdullah’s options are fast decreasing,” said political commentator Karim Raslan.

Tension escalated during the weekend over a crackdown aimed at government critics. On Friday, the government used Malaysia’s Internal Security Act, which permits detention without charges for up to two years, to arrest a well-known antigovernment blogger, Raja Petra Kamaruddin, and a popular opposition member of parliament, Teresa Kok. People held under the act have limited access to legal counsel.

Major opposition figures allied with Mr. Anwar, including influential Muslim politician Abdul Hadi Awang, challenged the detention of Ms. Kok, who was accused of complaining about noise from a mosque in her constituency. One opposition leader called the allegation “ludicrous.”

Also detained under the act was Tan Hoon Cheng, a local journalist who first reported remarks by UMNO politician Ahmad Ismail aimed at Malaysia’s minority ethnic Chinese population. The remarks, deemed racist, caused a national uproar in this multiethnic country and forced the party to suspend Mr. Ahmad for three years.

Ms. Tan was released Saturday. Malaysian Home Affairs Minister Syed Hamid Albar said she had been detained to ensure her safety after threats had made been against her.

The government also moved against Malaysia’s press, threatening to close three news media outlets — including Ms. Tan’s influential Chinese-language newspaper, Sin Chew Daily — for allegedly stirring unrest by reporting on “sensitive” issues such as race relations in Malaysia, where politically dominant ethnic Malay Muslims make up about 60% of population.

On Saturday, Mr. Syed Hamid defended the actions, saying they were needed to preempt racial conflict. He also denied the crackdown was meant to hamper Mr. Anwar’s bid for power.

In the interview, Mr. Anwar said the arrests were “a desperate act” to deflect attention from “internal strife within UMNO.” THE WALL STREET JOURNAL