The Islamic Resistance Movement (Hamas) must disarm before participating in the Palestinian parliamentary elections due on July 17, Raanan Gissin, an aide to Israeli Prime Minister Ariel Sharon said Tuesday.

The steps Palestinian leader Mahmoud Abbas has taken so far are not enough to convince Israel to move forward with the US-backed "roadmap" peace plan, Gissin said.

"We are not getting involved in Palestinian politics, but we are saying that if Hamas participates in the elections and remains an armed group then we won't be able to advance in the peace process," Gissin said.

Palestinians cannot move toward democracy if they allow a group with a "private army" to participate in elections, he added. Earlier polls said Hamas is likely to win the July election.

Israel was criticizing Abbas for his refusal to disarm militant groups by force as a latest round of violence is threatening a three-month-old ceasefire.

Abbas tried to avoid a large-scale confrontation with militants, but recently adopted a tougher approach, warning last week he will use "iron fist" against those violating the cease-fire.

"It is inconceivable for an armed party to participate in the democratic process; from there, it is impossible to move on to the roadmap, Sharon said after meeting with visiting US senators Bill Frist and Joseph Lieberman on Monday.

A similar message was conveyed by Foreign Minister Silvan Shalom in his meeting with Quartet economic envoy James Wolfensohn. "If Hamas wants to become a political party, it must disarm," Shalom said.