Palestinian security forces began a series of raids in the Gaza Strip (search), seizing weapons, shutting down two smugglers' tunnels between Egypt and the Gaza Strip, and arresting at least 12 smugglers, a Palestinian security official said Saturday.

It was not clear whether the raids marked the start of a clampdown on militants demanded by Israel and the United States. Such a campaign could help defuse growing tension, triggered by a Hamas bombing of a Jerusalem bus this week and the killing of a Hamas (search) leader in an Israeli missile strike.

The violence threatens to sink a U.S.-backed "road map" peace plan (search) that envisions Palestinian statehood by 2005.

Israeli Foreign Ministry official Gideon Meir (search) said Saturday's action was not enough, and Israel expects Palestinian security chief Mohammed Dahlan to arrest those involved in violence against Israel.

"We expect Dahlan to take his 20,000 troops and to start making arrests of the terrorists," he said. "We don't need any more words."

In a political development, the central committee of Yasser Arafat's (search) Fatah movement nominated longtime Arafat aide Lt. Gen. Nasser Yousef for the post of interior minister, said Hany Al-Hassam, one of 12 committee members.

The interior minister has broad responsibility for security matters, and Palestinian Prime Minister Mahmoud Abbas, who currently holds the role, asked Dahlan to assume some of those duties. It was unclear how the nomination, which still must be approved by the legislative council, would affect Dahlan's position.

Palestinian legislator Saeb Erekat said the closing of the tunnels reflects the Palestinian Authority's determination to enforce the law.

"The obstacle to this (crackdown) now is the Israeli policy of incursions, assassinations, building walls and noncompliance with the road map," he said.

Thirteen suspects were arrested during the Gaza raids, police said. Palestinian security officials said at least 12 of them were arrested for smuggling weapons.

An Israeli security source, speaking on condition of anonymity, said Dahlan ordered stepped-up patrols in the northern Gaza Strip to prevent the firing of homemade rockets at Israel. Such rocket fire in recent days prompted Israel to send tanks to the edges of Gaza, signaling that it might retake parts of the strip if shelling continues.

The official said American diplomats notified Israel of Dahlan's pledge to close the tunnels.

"This week, he will take control of Hamas and Islamic Jihad installations in Gaza and will confiscate their weapons," he official said.

The security forces closed the two tunnels Saturday night with sand, rocks and cement. They had been used for smuggling weapons and drugs from Egypt into the Gaza Strip at the southern town of Rafah.

The closing of the tunnels was one of the least controversial moves available to Palestinian security forces. Residents in the area complain about smuggling and periodic blasts when the Israeli army blows up the passages.

Several arrests were made in Rafah, officials said. In one incident, police were stoned by relatives of a detainee, witnesses said.

Earlier Saturday, Israeli troops fired rubber bullets at Palestinian stone throwers, injuring 16, in the West Bank town of Nablus.

The death toll from Tuesday's Hamas suicide bombing on a Jerusalem bus rose to 21 as a 70-year-old Israeli woman died of her injuries Saturday. The attack prompted Israel to kill a Hamas leader, and Islamic militants in turn threatened a wave of new attacks.

Palestinian leaders appealed for international intervention, urging the United States and other countries to help broker a truce following a week of violence.

"We've reached a point where the situation is in urgent need of foreign intervention so that we can return to the political track," Palestinian Information Minister Nabil Amr said after a Cabinet meeting in the West Bank town of Ramallah.

However, several previous cease-fire negotiations, including those led by former President Clinton and by CIA chief George Tenet, have failed.

A temporary cease-fire declared by militant groups two months ago dissolved following Israel's killing of the senior Hamas leader Ismail Abu Shanab on Thursday.

Israel said it was not interested in signing new agreements while the Palestinians have yet to live up to commitments under the road map, which calls for the Palestinians to dismantle militant groups.

The peace plan calls for an immediate end to violence, an eventual construction freeze in Israeli settlements in the West Bank and Gaza Strip, and the immediate dismantling of settlement outposts.

Palestinian legislator Saeb Erekat met Saturday with U.S. envoy John Wolf and urged the United States to pressure Israel to halt killings of militants.

On Friday, the United States froze the assets of six Hamas leaders and five European-based organizations that it said raise money for the group. Five Americans were among those killed in the Hamas bombing.

A prominent Hamas leader, Abdel Aziz Rantisi, lashed out at President Bush, calling him "Islam's biggest enemy" in comments carried by Dubai-based satellite channel Al-Arabiya.

Rantisi called the U.S. decision to freeze assets "a theft of Muslim money by the Americans."