By Luke Baker JERUSALEM, Dec 12 (Reuters) - The killing in Gaza of three children whose father was an intelligence aide to Palestinian President Mahmoud Abbas has sharpened tensions between Abbas's Fatah movement and Hamas, raising renewed fears of civil war. It also adds pressure on Abbas to make a decision soon about what to do with Hamas, which has led the Palestinian government since March but has largely been unable to govern because of sanctions against its Islamist administration. While Abbas has repeatedly indicated that he could call for new elections if Hamas does not drop its policy of non-recognition of Israel and find a way to form a unity government with Fatah, he has so far failed to act. In any debate about the crisis in Palestinian politics, the first point Hamas makes is that it came to power legitimately after winning free and fair elections. That fact leaves Abbas in jeopardy. If he dissolves the government and calls for new elections, he could be seen to be subverting the will of the majority. And if new elections are held, Hamas could easily win again. It is a conundrum that has perplexed Palestinian politics for months, contributing to the standoff between Hamas's and Fatah's armed factions, the steady breakdown in law and order and the threat in recent days that Gaza could topple into chaos. Monday's killing of the three boys, aged 6 to 9, as they were being taken to school highlights that the president must make a decision soon if a full-blown crisis is to be averted. "The president must act," said Azzam al-Ahmad, the head of Fatah's bloc in parliament. "He should take steps on the ground. He should not just issue appeals and make statements." Senior Abbas aides say he is expected to call for early elections in a speech on Saturday, but also leave the door open for further negotiations with Hamas to try to form a coalition government that would replace the current administration. It is more or less the same tactic Abbas has been employing since May, shortly after Hamas came to power, when he threatened to call a referendum on holding new elections if talks failed. The talks failed, but no referendum has been held. Unless he is explicit, the risk is that the speech will only confirm the status quo: Hamas in power and trying to find the funding to keep its government functioning despite sanctions. CIVIL WAR? At the moment, Hamas appears to be having more success in attracting funds from Arab neighbours and allies such as Iran than Abbas and his backers, including the United States, appear to be having in breaking the back of the Islamists. In the past two weeks alone, Palestinian Prime Minister and senior Hamas leader Ismail Haniyeh has managed to secure financing of up to $350 million from Iran and Qatar. That has bolstered Haniyeh's sense of security. Whereas a few weeks ago he agreed to step down as prime minister if a unity government were formed, now such a move appears less likely and Iran has encouraged him to stand firm. Haniyeh has also warned that if Abbas does call for new elections and they are held, it could lead to deeper unrest. Polling shows that Hamas's popularity has only marginally been eroded since it won elections in January. The group's supporters are keen for Haniyeh to remain prime minister. In a poll conducted in September, Khalil Shikaki, the head of the Palestinian Center for Policy and Survey Research, found that if elections were held right away, Hamas would likely win. With the prospects of forming a unity government slim given Hamas's rigidity and previous failures, Abbas has tough choices. If the president calls for elections and they are held, there is every possibility he and Fatah will not do as well as hoped. And if they are held and Fatah does do well, there is a very real threat of more fighting and even civil war. Tit-for-tat killings by rival Fatah and Hamas militant groups in the past two days have underlined the civil war threat, although experts say such an outcome is unlikely. "We are very, very far from civil war," said Raji Sourani, a lawyer and founder of the Palestinian Centre for Human Rights. "I'm not saying that there's something special or unique about us as Palestinians, but the internal ingredients just aren't there for a civil war to occur between us." (Additional reporting by Mohammed Assadi in Ramallah)