Kharas delivered his sermon at the al-Khadra mosque in the old city of Nablus, where earlier in the day Israeli troops had mounted a raid against Palestinian fighters.
Kharas said: "Israel soldiers invaded Nablus for two days. Where is the government to defend the old city?
"Where is the government that demanded the dismantling of the armed brigades? America will be defeated in Iraq and the believing Muslims will come here victorious."
Many West Bank mosques were being closely followed by authorities and some preacher respected Fayyad's call.
At a mosque in the city of Ramallah, where two police cars were parked outside, the preacher stuck to generalities, without getting into politics,.
"The refusal by the US, EU et al to deal with Hamas reflects their disrespect for the wishes of the Palestinian people"
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In Jenin in the northern West Bank, the regular pro-Hamas preacher was replaced by a clergyman who spoke of the need to support the new Palestinian leadership.
In 1996, then-Palestinian leader Yasser Arafat cracked down on Hamas preachers following a series of Hamas suicide bombings in Israel.
He monitored them closely and those considered too outspoken lost their jobs.
Kharas was one of them and he only returned to the pulpit last year, after Hamas' election victory.
He said he feared no one and would not change his ways even if it cost him his job.
"All my life, I preached and talked about Jihad (holy war)," Kharas said.
Jacky Rowland, Al Jazeera's correspondent in Ramallah, said: "The government knows how important the mosques are in forming public opinion.
"It may manage to curb the influence of Hamas, but to eliminate it from the mosques altogether is another matter."