President Michel Aoun says that Lebanon would seek evidence and documents from the United States that led Washington to impose sanctions on Gebran Bassil, a prominent Christian politician who is his son-in-law.
The United States on Friday blacklisted Bassil, leader of Lebanon's biggest Christian political bloc, accusing him of corruption and ties to the Iranian-backed Shi'ite Hezbollah movement that Washington deems a terrorist group.
Aoun asked Lebanon's caretaker foreign minister to obtain the evidence and documents that should be submitted to Lebanon's judiciary "to take the necessary legal measures" if any data is available, said a statement tweeted by the presidency on Saturday.
Bassil heads the Free Patriotic Movement founded by Aoun and has served as minister of telecoms, of energy and water and of foreign affairs. He said on Friday that sanctions did not scare him and that he had not been "tempted" by promises.
Hezbollah condemned the US move as blatant interference aimed at forcing "American conditions and dictates" on Lebanon.
The sanctions could complicate efforts by Prime Minister-designate Saad al-Hariri to navigate Lebanon's sectarian politics and assemble a cabinet to tackle a financial meltdown, the country's worst crisis since its 1975-1990 civil war and which is rooted in endemic corruption, waste and mismanagement.
The US Treasury Department accused Bassil of being at the "forefront of corruption in Lebanon". A senior US official said Bassil's support for the armed group Hezbollah was "every bit of the motivation" for targeting him for sanctions.
The FPM has a political alliance with Hezbollah, which has become Lebanon's most powerful political force, and Bassil has defended the group as vital to the defence of Lebanon.
Bassil was sanctioned under the Global Magnitsky Human Rights Accountability Act, which targets human rights abuses and corruption around the world.