Seventeen Afghans with alleged links to the Taleban and al-Qaeda have been arrested in south-west Pakistan.
They were held in raids on Thursday night in Quetta, capital of Balochistan province, police said.
Some held "important positions" during Afghanistan's Taleban regime, Balochistan's police chief said.
Pakistan, a key ally in the US-led war on terrorism, has detained hundreds of al-Qaeda and Taleban suspects since the fall of the regime in December 2001.
Balochistan police chief, Chaudhry Mohammed Yaqub, said the arrests were made in three neighbourhoods of Quetta following a tip-off.
"We have also heard that these people were involved in conspiracies against the Afghan government," he said.
"Right now, these people are in our custody. They are being interrogated and everything will be clear in a day or so."
A number of the arrested suspects were named - Mullah Abdur Razzaq, Mullah Sher Dil, Mufti Rehmat Ullah and Mullah Ibrahim.
Mullah Dil is the former deputy governor of the southern Afghan province of Helmand and Mullah Ibrahim the former chief of Taleban police in Kabul, police said.
However, Mullah Akim Latifi, a senior Taleban official, told the Associated Press no former government officials or Taleban leaders had been arrested.
"There is no truth in this claim. Our people live in Afghanistan, not in Pakistan," he said.
Dozens of supporters of the hardline Islamist alliance, the Muttahida Majlis-e-Amal, protested in Quetta at the arrests, saying the authorities were victimising religious leaders.
Balochistan was the early base for the Taleban before it seized control of most of Afghanistan in the mid-1990s.
Balochistan has also seen a recent upsurge in violence from tribal groups demanding more autonomy and a greater share of provincial wealth.
Mr Yaqub said it was not yet known whether the arrested suspects were involved in the violence.