GAZA, Jan 20: Amid US concern at slow progress in finding the killers of three Americans in the Gaza Strip last year, a Palestinian security chief involved in the hunt blamed Israel on Tuesday for obstructing the investigation.

Colonel Rashid Abu Shbak said information was still coming in and the investigating team had been upgraded, but he had no new leads on who was behind a roadside blast that tore into a diplomatic vehicle on Oct 15, killing the security guards.

The failure to find the attackers has further complicated relations between the Palestinians and Washington, which already accuses them of not doing enough to crack down on militant groups in line with a blueprint for peace.

Abu Shbak, the Palestinian Authority (PA) internal security chief in Gaza, said Israel was making the inquiry more complicated by repeated military raids into Gaza and was trying to persuade the United States that the Palestinians were not serious.

"The Israeli deeds and the Israeli practices on the ground complicate the mission," he said in an interview in Gaza City. "But the Americans are not naive. The Americans are in daily and serious cooperation with the Palestinians. They are partners in the investigation."

Israel says Gaza is one of the few places where the operational capability of the Palestinian forces is still largely intact. "Daily I receive new information from the team regarding the issue and President Yasser Arafat has broadened the investigation committee and upgraded the level," Abu Shbak said.

"It's a signal of the concern of the president and an indication of our seriousness." US officials have been stopped from going to Gaza since the attack, making it more difficult to assist aid programmes for the Palestinians. No decision has been taken yet on when they might be allowed to return.

"We want to see more progress on the investigation and we are not satisfied with what we have seen so far," one US official said. Three people have been held for questioning since last October and many others have been brought in and released, but nobody has been arrested for direct involvement in the incident.

There has been no claim of responsibility from any of the militant groups battling Israel for more than three years and behind scores of roadside attacks and suicide bombings.

"There is nothing consistent in security, sometimes you stop in front of a closed door and minutes later the door is opened," Abu Shbak said. "Sometimes this door is opened because of tiny information that was not relevant at the beginning... I am confident that in the end this effort is going to lead to a result."- Reuters