The number of letters containing poisonous substances Friday continued to target the Supreme Court judges.

According to sources, the number of top court judges who received the toxic letter has reached 10.

The SC judges who received the suspicious letter today are Justice Ayesha Malik,  Justice Irfan Saadat Khan, Justice Muhammad Ali Mazhar,  Justice Syed Hasan Azhar Rizvi and Justice Muneeb Akhtar,  the sources said.

They said the letter had been handed over to the Counter Terrorism Department (CTD)

“Arsenic powder has also been found on these letters,” the sources said.

Earlier, toxic letters targeted Chief Justice of Pakistan Qazi Faez Isa and four other judges.

Authorities have put post offices and courier companies on alert. The post office officials and courier services have been asked to be vigilant and check thoroughly any letter sent to any high-profile personality.

Sources said that all the post offices and courier services were directed not to open any 'suspicious' letter addressed to high-profile personalities.

Prime Minister Shehbaz Sharif said yesterday that the government was investigating the matter regarding the letters received by judges with suspicious powder. 

“The government, with the sense of responsibility, will also probe this matter to uncover the reality,” the prime minister said while addressing his cabinet.

In the ongoing investigation by the Counter Terrorism Department (CTD), the close-circuit television (CCTV) cameras near the post office have been checked but still, no to no avail. 

The sources also said that the work on the validity of the names and addresses of senders is being checked.

The preliminary investigation into the threatening letters received by the senior judges has revealed that they were sent from the same place.