President Bush called Lebanese Prime Minister Fuad Saniora on Wednesday to express his condolences for the assassination of a cabinet minister whose death has heightened tensions between the country's mostly anti-Syrian government and the Islamic militant group Hezbollah.

"President Bush reiterated to Prime Minister Saniora the unwavering commitment of the United States to help build Lebanese democracy, and to support Lebanese independence from the encroachments of Iran and Syria," said Gordon Johndroe, a spokesman for National Security Council at the White House.

Bush also called the father of the slain leader, former Lebanese President Amin Gemayel. Gemayel's son, Pierre, was gunned down in his car on Tuesday in Beirut. Pierre Gemayel, who strongly opposed Syrian influence in Lebanon, was the minister of industry.

The U.S. has accused Syria and Iran of plotting to topple Saniora's government, which is dominated by politicians opposed to Syrian meddling in Lebanon. Bush and other U.S. officials have stopped short of specifically blaming Iran or Syria for the assassination, but the president called for a full investigation to identify "those people and those forces" behind it.

Bush wants the U.N. Security Council to move quickly to establish a special tribunal to investigate the 2005 assassination of former Prime Minister Rafik Hariri. The Council is facing a deadline to approve a letter endorsing an agreement with Lebanon to create a tribunal.

Johndroe said that in his phone calls, Bush said that "violence and unrest in Lebanon will not stop the international community from establishing the special tribunal for Lebanon."

Hezbollah leader Sheik Hassan Nasrallah, meanwhile, has urged his followers to prepare for mass demonstrations to topple the U.S.-supported government headed by Saniora if it ignores Hezbollah's demands to form a national unity Cabinet. Hezbollah, an ally of Syria, gained political strength in the country as a result of the war it fought last summer against Israel.