The World Baloch Organisation said the latest drive will see more than 100 London buses with adverts carrying slogans like "Free Balochistan", "Save The Baloch People" and "Stop Enforced Disappearances" from this week.
"This is the third phase of our London campaign to raise awareness about Pakistan's human right abuses in Balochistan and the right of the Baloch people to self-determination. We started with taxi adverts, then did roadside billboards and now we are advertising on London buses, said Bhawal Mengal, spokesperson for the organisation.
"This is a peaceful advertising campaign. Pakistans aggressive reaction is a bare-faced attempt to intimidate the UK government and Baloch human rights defenders, said Mengal.
The advertising campaign has been backed by British human rights campaigner, Peter Tatchell, who said Pakistans attempts to prevent them amounted to "censorship" and anti- democratic.
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"These adverts are much needed to defend the human rights of the Baloch people and to expose the atrocities of the Pakistani military and intelligence agencies, he said.
Baloch people argue that they are ethnically and culturally different from the rest of Pakistan and have been campaigning for an independent nation for years.
Pakistan dismisses any notion of a "free Balochistan" as an attack on its sovereignty.
Pakistan on November 3 had summoned the British High Commissioner in Islamabad to protest over the "Free Balochistan" slogans displayed on London cabs that it said attacked the country's territorial integrity and sovereignty.
Balochistan is the largest of Pakistan's four provinces, but people in the restive region have long complained that they do not get a fair share of its natural resources.
The organisation describes itself as a non-violent and democratic international membership organisation dedicated to defending the Baloch peoples' political, social and cultural rights.