President Bush called acting Prime Minister Ehud Olmert on Thursday, speaking with him for the first time since Prime Minister Ariel Sharon suffered a massive stroke last week.

Bush expressed concern for Sharon, who remained in critical but stable condition. Sharon and Bush formed a strong relationship in the past five years.

"He expressed our deep concern regarding the illness of Prime Minister Sharon," National Security Council spokesman Fredrick Jones said, describing the call. "He stated that our thoughts and prayers are with the prime minister's family, the Israeli government and the Israeli people. He wished acting Prime Minister Olmert well in these difficult circumstances."

White House officials did not rule out the possibility of Olmert visiting the United States but indicated Bush did not extend an invitation Thursday. Israeli officials said Thursday that Olmert may soon visit the White House.

Bush also said he would continue to implement the joint vision he and Sharon had for promoting Middle East peace, according to a statement from Olmert's office. He asked Olmert to tell Sharon's sons, Omri and Gilad, that Bush admires their father and wishes him the best.

Bush also said the militant Palestinian Hamas group, which is running in Jan. 25 parliamentary elections, must change its approach to Israel and recognize the Jewish state's right to exist, the statement from Olmert's office said.

Olmert told Bush he admired his perseverance in fighting terrorism, according to the statement.