Cricketer-turned-politician Imran Khan has begun a march to Pakistan's restive tribal areas to protest against US drone strikes, reports the BBC.
The two-day march started in Islamabad and is due to end in South Waziristan, a major focus of strikes.
Khan expects large numbers to join him. It is not clear if authorities will allow the march to reach its goal.
Khan, like many Pakistanis, says the attacks kill large numbers of civilians and foster support for militants.
US officials insist strikes by the unmanned aircraft rarely claim civilian casualties and are an effective weapon against the Taliban and al-Qaeda.
The BBC's Orla Guerin in Islamabad says it is unclear how far the convoy will be able to get.
Pakistani authorities have expressed security concerns and they may stop the march before it reaches the tribal areas, she says.
Khan's Pakistan Tehreek-e-Insaf (PTI) party says the march and rally will attract hundreds of thousands of people.
"When they think of Waziristan, quite rightly, people get a bit scared because what is happening there is a mess created by this so-called war on terror, which has become a war of terror," Khan said.
"And it has collateral damage... women and children getting killed, families getting killed. [This] has created militants."
Khan's critics accuse him of trying to boost his party's popularity but supporters say the march shows he is in touch with the concerns of Pakistani people.
Mohammad Ansar Adnan, a student in Islamabad, told Reuters news agency that drone attacks were "an escalating problem".
"If Imran Khan is taking a step to resolve this issue, I think we should all go along with him, and once we are there, we should offer prayers for peace."
Authorities in South Waziristan say they have not given the PTI permission to stage a rally and they cannot provide security for so many people.
The government of Pakistani President Asif Ali Zardari says drone strikes are counterproductive and a violation of its sovereignty.
However, it has done nothing to stop them and many Pakistanis - including Imran Khan - believe this amounts to tacit consent.
In September, a report by Stanford and New York Universities in the US said Pakistani civilians were being "terrorised" 24 hours a day by CIA drone attacks.
It said rescuers treating casualties were also being killed and wounded by follow-up strikes.
The scale of civilian deaths has been difficult to assess because independent media and researchers are denied access to the tribal areas.
US President Barack Obama has insisted that the drone strategy is "kept on a very tight leash" and that without the attacks, the US would have had to resort to "more intrusive military action".