Jerusalem ? South Africa on Thursday joined a growing list of countries inviting Hamas leaders for talks, raising Israeli concerns that the international front against the Islamic militants is crumbling.

As Hamas pressed on with efforts to form a Palestinian government and gain world support, Palestinian President Mahmoud Abbas warned that al-Qaida terror operatives are trying to infiltrate the West Bank and Gaza.

Acting Israeli Prime Minister Ehud Olmert said Thursday that Israel also was monitoring the al-Qaida efforts.

Israel considers the Islamic terror threat as a main security challenge, but the equation has changed since Hamas swept to victory in Palestinian parliamentary elections in January.

Israel has been trying to isolate Hamas to counter the effect of its imminent rise to power in the neighboring Palestinian territories. Israel’s efforts absorbed a blow when Russia invited Hamas leaders for talks, due to begin today.