Islamabad: US Assistant Secretary of State for South Asian Affairs Richard Boucher arrived here today on an unannounced visit to Pakistan, three days ahead of the expected return of the exiled former Premier Nawaz Sharif to challenge the rule of President Pervez Musharraf.

The US embassy said Boucher is visiting Pakistan for the bilateral Strategic Dialogue, which was in cold storage for some time. He came here ahead of the visit of Deputy Secretary John Negroponte, who is scheduled to arrive on September 12 to discuss a host of issues, including the political crisis faced by Musharraf and his plans to get re-elected in the coming weeks.

During their visits here two months ago, Nagroponte and Boucher had said US had no objection to Musharraf continuing as the Army Chief even after his re-election as President.

Significantly, Boucher's visit this time came three days ahead of the expected return of Sharif and his brother Shabaz from their exile. The Sharif brothers have fixed September 10 as the date for their arrival in Islamabad, following a landmark Supreme Court verdict allowing them to return home.

The Musharraf government plans to either send them back to Saudi Arabia where they were exiled to in 2000 or arrest them over the corruption and criminal cases against them, which were being reopened.

The government claims that the Sharifs had been sent to exile on the promise that they would not return before 10 years. The Saudi government, which provided the asylum to the Sharifs, was reportedly upset over their decision to return.