(Reuters) - The coming rise of Islamism in the Arab world will strengthen support for the Palestinian Islamist movement Hamas, which will not give up its armed confrontation with Israel, senior Hamas official Mahmoud Al-Zahar said Monday.

If Western-backed Palestinian President Mahmoud Abbas bets on peace talks with Israel rather than reconciling his Fatah movement with Hamas, he will lose out, Zahar said in an interview with Reuters in his Gaza office.

Fatah and Hamas have been bitter enemies since 2007 when the Islamists expelled Fatah and seized control of the Gaza Strip, which has been under Israeli blockade ever since.

"The changing factors around us are in our favor ... they are not in favor either of Fatah's project or those with whom it cooperates, including the Israeli enemy," he said, watched by his bodyguards.

"It all depends on Fatah's policy now," Zahar said. "If Fatah wants the (unity) agreement to be accomplished, we will be ready. If they do not want, then we are sitting here and the future is ours."

Zahar said Hamas was not prepared to relinquish the fight against Israel under any circumstances. He denied that Hamas leader Khaled Meshaal, based in Damascus, had endorsed Abbas's concept of non-violent "popular resistance" against Israel.

"Popular resistance includes both Fatah agenda, which speaks of protests only, and the Hamas position which advocates gathering all means of military armament for the sake of self-defense," Zahar said.

He foresaw a rising tide of Islamism in the Arab world which would strengthen the Palestinian cause.

"What is coming in Egypt, in Tunisia, in Libya and currently in Sudan is supportive of the Palestinian cause, not as in the past a strategic supporter of the Israeli occupation," he said.

"What is coming is a thousand times better than in the past. Therefore we have to invest in these achievements by the Arab street for the sake of achieving the fundamental goals of the Palestinian people, the liberation of land and the return of (refugees)," Zahar added.

Since their 1979 peace treaty Egypt, along with Jordan, has been Israel's most reliable Arab partner in the Middle East. But the overthrow last February of Egyptian president Hosni Mubarak in the uprising inspired by popular revolution in Tunisia has created uncertainty over Egypt's future attitude toward Israel.

NO TO NON-VIOLENCE

Zahar is a leading Hamas figure, seen by Fatah as a hard-liner, who lost two sons in the fight against Israel. He is a senior negotiator in the reconciliation process with Fatah, which has been faltering almost since it was signed.

Zahar said Egypt, now ending a lengthy election process that will lead to a new constitution, is clearly destined to be ruled by "a sweeping Islamist party and a nationalist party" that will back the Palestinian cause.

The reconciliation agreement with Fatah, signed last May and sealed personally by Abbas and Meshaal last month in Cairo, may suffer if Abbas pursues peace talks with Israel, he warned.

Senior officials of the two sides have held talks in Amman, Jordan, in the past week after more than a year in suspension. "Our doubts are really great, especially after these meetings in Amman," Zahar said.

Hamas opposes acceptance of Israel and is ostracized by the West as a terrorist group which refuses to renounce violence. Israel has warned that striking a unity pact with Hamas would eliminate Abbas and Fatah as a potential partner for peace.

"Imagine that the Israeli enemy attacked us today or tomorrow ... If we were attacked we would respond by all possible means," Zahar said.

If Israel launched a military offensive into Gaza, Zahar said he bet Arab reaction would be stronger than in 2009 when 1,400 Palestinians were killed in Israel's three-week onslaught to stop rocket firing from Gaza into its territories. Thirteen Israelis were killed in that conflict.

"(Israel) could use the foggy political situation as the Arab nation still organizes itself ... to launch a new aggression against Gaza Strip," he said.

"They cannot accept that Gaza remains a painful and dangerous thorn in the future of the Israeli entity."