Image copyright AFP Image caption Bilawal Bhutto Zardari spoke from the same bus that his mother was killed in

Tens of thousands of Pakistanis have attended the first mass rally held by the son of murdered Prime Minister Benazir Bhutto.

Bilawal Bhutto Zardari, 26, is tipped to become the next leader of the People's Party (PPP), currently headed by his father Asif Ali Zardari.

He told supporters in Karachi: "If you want to save Pakistan, the only answer is Bhuttoism and the PPP."

He had previously been forced to keep a low profile because of Taliban threats.

The BBC's Shahzeb Jillani in Karachi says that for weeks, life-sized pictures of the Bhutto dynasty have featured on billboards all over Karachi.

They show Mr Bhutto Zardari, Benazir Bhutto and his grandfather, Prime Minister Zulfikar Ali Bhutto - Pakistan's first democratically elected leader, who was hanged by the army in 1979.

Image copyright AFP Image caption Organisers say more than 100,000 people attended

Shahzeb Jillani, BBC News, Karachi

Karachi has not seen such a huge PPP rally for years. The party is trying to show that it still has mass appeal, and can compete with other opposition politicians such as Imran Khan. It is, after all, a party that has fought military dictatorships in Pakistan time and again over the last four decades.

But in the end, the rally was seen as a government-sponsored event, because the party still governs the southern province of Sindh. Many of the tens of thousands of people who attended were bussed in from the party's rural strongholds.

They came to hear their young leader Bilawal Bhutto Zardari, in whom many party loyalists see a reflection of his assassinated mother, Benazir Bhutto. There was little substance in his speech, though he made some bold points about the need to fight militancy and protect religious minorities.

He attacked political opponents across the political spectrum, but he said nothing about how he plans to tackle allegations of corruption and improve governance in Sindh.

Image caption Most of those attending were party loyalists from Sindh

Our correspondent says there was a festive mood among PPP workers, many of whom have travelled by bus from rural areas of Sindh province, which is governed by the party.

The organisers say the event was attended by more than 100,000 people.

Everyone attending the rally had to undergo a security screening, and cars are being banned from travelling nearby.

In the run-up to the May 2013 general election, Mr Bhutto Zardari could not hold public gatherings because of threats to his life.

The party, which had governed since 2008, lost the election after being blamed for misrule and accused of corruption and being out of touch.

More recently, the PPP appears to have lost more ground to opposition politicians such as Imran Khan, our correspondent says.