Pakistan on Sunday sounded a high alert at airports, clamped prohibitory orders and detained thousands of opposition activists as former prime minister Nawaz Sharif faced the threat of deportation immediately after his return from a seven-year exile on Monday.

As per a plan chalked out by Pakistan government, the plane carrying Sharif brothers will be allowed to land, but the brothers will later be deported to Saudi Arabia where they were initially sent to exile in 2000, a year after the bloodless coup by General Pervez Musharraf [Images], officials were quoted as saying in Islamabad.

Railways Minister Sheikh Rashid Ahmad had earlier said Sharif will be detained after his arrival in Islamabad and 'deported' to either Britain or Saudi Arabia.

Sharif, 57, could be deported back in a special Saudi plane, which may arrive on Sunday itself as Sharif brothers were set to land in Islamabad by Gulf Air flight from London [Images] around 1130 hrs IST on Monday, the officials said.

The two brothers would be allowed come out of the plane, will be ushered in to a lounge and would be taken to the special plane and deported, they were quoted as saying by Dawn TV.

The government has declared a red alert at airports. A five km radius around the Rawalpindi and Islamabad airports will be sealed and no one, including media and political workers, will be allowed to enter the area.

Authorities have clamped Sec 144 in nearby Rawalpindi to thwart attempts by Sharif's supporters to converge there.     

PML-N spokesman Ahsan Iqbal said over 2,000 people have been detained in a government crackdown on Sharif's supporters.

Besides Sharif's PML-N, leaders of All Party Democratic Movement, which included Islamist alliance Muttahida Majilis Amal, and cricketer-turned-politician Imran Khan have appealed to their partymen to receive Sharif brothers.

The government has warned police officials in Rawalpindi and Islamabad that they will be suspended for 'dereliction' of duty if they failed to stop Sharif supporters.

Bhutto's Pakistan People's Party welcomed Sharif's decision to return but said that it will stay away from taking part in welcome ceremonies.

The government was confident that it could defend its action before the Supreme Court, which had last month ruled that Sharif's return should not be obstructed, officials said.

The government would defend itself saying that they were not arrested but deported as per the 2000 deal they struck with Saudi Arabia.

The plan was chalked out after Saudi prince and intelligence chief Muqrin bin Abdul Aziz said in Islamabad on Saturday that Riyadh was ready to host them again.

'Saudi Arabia will welcome the Sharifs if they are deported by the Pakistani government,' The News quoted him as saying after a meeting he had along with Lebanese leader Saad Hariri who negotiated the exile for Sharif in 2000.

To a question, Aziz had said Musharraf did not raise the issue of sending Sharifs back to Jeddah where they lived for six years.

'Saudi Arabia is for all our brothers and sisters all over the Muslim world,' Aziz reportedly said later to a specific question whether they could be deported again.

Sharifs' estate being readied:

The 450-acre sprawling Sharif estate at Raiwind in Lahore [Images] is bustling with activity as it awaits the return of former Prime Minister Nawaz Sharif and his brother Shabaz.

The estate, which has a variety of fruit orchards besides cultivable land and luxuriously built houses for Sharif brothers, was the nerve centre during the heydays of their rule before the PML-N chief was overthrown.

It was virtually the Prime Minister's Office's base camp but receded to background after the Sharifs were deported to Jeddah in Saudi Arabia along with 20 members of their family.

Over 100 workers have been employed in the estate who are looking forward to the return of Sharifs and the days of glory to the estate.

While Sharif's party, the Pakistan Muslim League-N, tried to mobilise its supporters across the country to receive Sharif's when they land in Islamabad tomorrow, the estate has been kept ready for their stay just as the government might decide to keep them under house arrest.