Weapons experts in Palestinian terror groups who have undergone training in Lebanon, Syria and possibly Iran have recently infiltrated the Gaza Strip, a senior security official said.

The official said that after Israel pulled out of Gaza, several Palestinians who had attended training camps run by Iranians and Hezbollah members entered the Strip, apparently from Sinai. Both Iran and Hezbollah have invested a lot of effort during the last few years in assisting terror organizations in the West Bank and Gaza, helping them manufacture explosives and high-trajectory weapons such as Qassam rockets and mortar shells.

In the past, vast technological knowledge has been transmitted via the Internet or via memory chips used in laptop computers. In a few cases, the Shin Bet security service has managed to keep Palestinian and Israeli Arab couriers from smuggling instructions for manufacturing weapons into the territories. However, even when the instructions do reach the terror organizations, the groups have difficulty achieving significant operational improvements. That's why the Palestinians have recently decided to take advantage of the disengagement and focus on sending weapons experts themselves into Gaza, which has become easier to do since the pullout.

Most of the experts are Hamas members who specialize in making explosive devices and improving high-trajectory weapons - specifically, building warheads and improving the rockets' aerodynamics. Hamas is primarily concerned with upgrading its operational ability ahead of a possible renewed confrontation with Israel. At the moment, however, the organization in Gaza is for the most part heeding an agreement regarding maintaining the "calm" in the territories, at least until the Palestinian parliamentary elections at the end of the month.

Israel has also recently received information, not yet fully confirmed, that improved Katyusha rockets are being smuggled into the Gaza Strip. These rockets have a 20-kilometer range and a 6.3-kilogram warhead, and are more accurate than the Qassam rockets.

However, the effectiveness of the improved weaponry is still limited; Hezbollah and Palestinian terror groups have been firing similar rockets at Israel from Lebanon for many years, but without much accuracy.

In the West Bank, Hezbollah activity appears to have declined recently, as compared to that of Palestinian terror groups. In 2003 and 2004, Hezbollah was the most prominent cause of terror in the territories: The Israel Defense Forces estimates that more than 70 percent of the terror attacks in the West Bank were initiated by the Lebanese group, which provided funding and general instructions for the attacks, most of which were carried out by Fatah and Islamic Jihad.

Security officials attribute the decrease in Hezbollah activity to several factors.

First of all, in contrast to its activity in Lebanon, "the organization worked on quantity instead of quality," said a security official. "The goal was to carry out as many terror attacks as possible. As a result, the Lebanese joined a lot of amateurish cells, a large portion of which we discovered with relative ease."

In addition, some Palestinian cells reported to Lebanon that they had carried out terror attacks - in return for which they demanded and even received money - although they had not actually done anything.

For these reasons, Hezbollah has decided to limit its activity in the West Bank. At the moment, the organization is making sure to demand confirmation of terror activity from the Palestinian cells with which it maintains contact. In addition, the Palestinian Authority has discovered that it is easy to "buy the silence" of terrorists who work with Hezbollah. Many of them - primarily members of Tanzim, which is affiliated with PA Chairman Mahmoud Abbas' ruling Fatah party - crossed over to work for the Palestinian security services in the past year, in exchange for a regular paycheck.