Anwar Ibrahim, the Malaysian opposition leader, has called a major rally of supporters, amid speculation that he is manoeuvring to oust the coalition government that has ruled the country for more than half a century.
The rally will be held on Monday evening at a stadium on the outskirts of Kuala Lumpur, the Malaysian capital.
Malaysia has seen rising political tensions in recent weeks, with the government of Abdullah Badawi, the prime minister, and opposition, led by Anwar, seen as nearing a showdown.
Anwar has vowed to topple the government at some point in September by orchestrating the defection of around 30 government MPs.
On Monday the government saw its first high profile departure when Zaid Ibrahim, the law minister, submitted his resignation over the arrest of three people under the colonial era Internal Security Act (ISA).
An opposition MP, a journalist from a Malaysian Chinese newspaper and a prominent blogger were all arrested on Friday under the ISA, which allows for indefinite detention without trial.
In comments published in Malaysia's New Straits Times newspaper before his resignation, Zaid said the ISA was "open to abuse".
"If we cannot be fair in implementing it, then we should confine its use to terrorists," the paper quoted him as saying.
"If we have to use the ISA to detain people, it shows that we have no confidence in our enforcement agencies."
|Abdullah's government has come under pressure since the March elections [AFP]
An aide to Zaid told the Associated Press news agency it was up to the prime minister to accept the resignation.
Abdullah's Barisan Nasional coalition government has come under severe pressure since the opposition won over a third of parliamentary seats in elections in March.
Anwar's opposition alliance now has 82 MPs in the 222-member parliament.
Anwar, who returned to parliament as an MP last month after a 10 year absence, said in an interview published on Monday that although his plans to take power on September 16 had been delayed, he would press ahead.
"My personal target is within September," Anwar told Monday's edition of the Asian Wall Street Journal.
Anwar has recently faced charges of sodomising a male aide similar to those which saw him sacked from the government in 1997 and subsequently jailed.
His conviction for sodomy was later overturned, although a conviction on a separate corruption charge still stands.
Opposition officials said they planned to deliver a letter to the prime minister's office on Monday seeking a meeting with him for a "peaceful power transition" to the opposition Pakatan Rakyat alliance.