The Office of the National Security Adviser (ONSA) has asked Nasir el-Rufai, former governor of Kaduna State, to submit any evidence he has regarding the alleged procurement of thallium sulphate, to the (DSS) for investigation.

Thallium sulphate is a highly toxic, colourless and odourless chemical capable of causing fatal poisoning in small doses.

In a letter dated January 30, 2026, and addressed to Nuhu Ribadu, el-Rufai claimed the substance was reportedly sourced from a supplier in Poland. He requested clarification over the alleged importation by ONSA.

In its response, ONSA denied the allegation, stating that it neither procured nor initiated any process to acquire thallium sulphate and has no intention of doing so. The office added that the allegation had been formally referred to the DSS for a comprehensive investigation and urged el-Rufai and any other individuals with relevant information to present evidence to the security agency.

The response, dated February 13, 2026, was written on behalf of the NSA by Brigadier-General OM Adesuyi. It was initially rejected when delivered to el-Rufai’s Abuja residence on Friday, reportedly due to the absence of the head of security, but was eventually received and signed for on Sunday.

In the letter, Adesuyi assured that all parties with relevant information would be invited by the DSS to assist in establishing the facts and ensuring due diligence.

Separately, el-Rufai had also alleged that he accessed an intercepted telephone conversation involving Ribadu. Speaking on Prime Time, an Arise Television programme, on Friday, he claimed that “someone tapped” the NSA’s phone and that he listened to a conversation in which Ribadu allegedly directed security operatives to arrest him.