Lebanon's Gebran Bassil is ready to separate his Free Patriotic Movement from Iran-backed Hezbollah with conditions, US ambassador to Lebanon Dorothy Shea said on Monday.
Ms Shea was speaking days after Washington imposed sanctions on the former minister and son-in-law to President Michel Aoun.
But she said the Christian ally of the Iran-backed party lacked understanding of US policy after he criticised the sanctions as unjust and politically motivated.
Mr Bassil said they were imposed after he refused to submit to a US demand to break ties with Hezbollah, because that would put at risk national unity and peace in Lebanon.
“Mr Bassil might think that leaking selective information out of context about our mutual discussion serves his cause," Ms Shea said.
"This is not the way I usually work, but I will reveal one thing: he himself expressed his readiness to separate from Hezbollah, under certain conditions.
"He actually expressed gratitude that the United States had got him to see how the relationship is disadvantageous to the party."
In 2006, Mr Bassil's party signed an alliance with Hezbollah, giving the party the much-needed backing of a major Christian faction to demonstrate inter-religious support for keeping its weapons.
Since then he has defended the heavily armed group as vital to the defence of Lebanon.
"We will not refute every inaccurate point made in Mr Bassil's speech," Ms Shea said.
"There were many of them, where there was a misunderstanding of how the sanctions worked and a lack of understanding of US policy and the way it was made.
"Even key advisers told me that they encouraged Mr Bassil to take this historic decision."
She said the sanctions were on Mr Bassil, not his party, and that the US "does not punish or destroy the Free Patriotic Movement".
After Washington's move on Friday, Mr Aoun called on the Foreign Ministry to formally request any documents as evidence of Mr Bassil's alleged corruption, so the Lebanese judiciary could investigate and file charges if needed.
“All I can say is that we seek to make the largest amount of information available when the names are released, but as is often the case, some of this information is not releasable," Ms Shea said.
She said Mr Bassil was welcome to challenge the US move in the American legal system.
The US "took this measure in solidarity with the Lebanese people who, for more than a year, have demanded their political leaders to end business as usual by working to chart a new direction devoted to reform and transparency, and uprooting rampant corruption from its roots", Ms Shea said.
Since last October, tens of thousands have protested in Lebanon demanding political reform, an end to corruption and competent leadership that can address the dire economic crisis.
On Sunday, Mr Bassil said he had been told by Mr Aoun that a senior American official had called him and said that the party leader must break its relationship with Hezbollah "immediately" or US sanctions would be imposed within four days.
He has held several positions in previous governments, including the communications minister, energy and water minister and foreign minister.
Mr Bassil is widely believed to hold ambitions of succeeding his father-in-law as president.