Former Pakistani leader Nawaz Sharif was scheduled to declare in London Thursday when he will return home from exile and challenge President Gen. Pervez Musharraf's plans to extend his rule.
The planned announcement comes a day after Benazir Bhutto, another exiled former premier and Sharif's archrival, said she was progressing toward an agreement with Musharraf that could see them share power.
Bhutto claimed Musharraf had agreed to step down as head of the army, ending military rule eight years after the general ousted Sharif in a bloodless coup.
The Supreme Court ruled last week that the conservative secularist Sharif, who has been in exile since 2000, and his politician brother can return to Pakistan.
Sharif was arrested when the army seized power in 1999. He was eventually sentenced to life in prison on hijacking and terrorism charges. He was released from jail a year later after signing a pledge not to return to Pakistan for at least 10 years.
Shahbaz Sharif told Pakistan's Geo television that his brother would announce details of their return on Thursday.
However, government officials have said that Sharif, who has denounced Musharraf as a dictator, could be re-arrested on reaching Pakistani soil on charges dating to the 1999 coup.
Musharraf had vowed to prevent both Bhutto and Sharif from entering Pakistan again, blaming them for corruption and economic problems that nearly bankrupted the country in the 1990s, when each had two turns as prime minister.
However, Musharraf has recently begun talking of the need for political reconciliation and an alliance of moderates to take on religious extremists.