Palestinian Authority policemen shot and killed two Hamas gunmen and arrested a third on Thursday during an exchange of fire in Kalkilya. A PA security officer was also killed in the shootout, the second of its kind in the city since the beginning of the week. Thursday's deaths bring to four the number of Hamas men killed by security forces loyal to PA President Mahmoud Abbas in the past few days. The two Hamas men killed early Thursday were all members of the movement's armed wing, Izzadin Kassam. The Hamas operatives killed on Sunday, Muhammad Samman and Muhammad Yassin, were also top members of Izzadin Kassam. The policeman who was killed in Thursday's confrontation was identified as Tarek Zandi, who works for the PA's Preventative Security Service - an apparatus that has been spearheading a massive crackdown on Hamas supporters and infrastructure in the West Bank over the past few years. In response to the killings, Hamas announced on Thursday that from now on, its militiamen in the West Bank would deal with Abbas's security forces as if they were "Zionist soldiers." The announcement is seen as a direct call on Hamas supporters in the West Bank to launch armed attacks on members and commanders of the PA security forces. The two incidents are seen as a sign of growing tensions between Hamas and Abbas's Fatah faction, which dominates the PA security forces in the West Bank. The clashes have also prompted Hamas to suspend its participation in Egyptian-sponsored talks aimed at ending the rivalry between the two parties. Like the previous incident, Thursday's confrontation began when a PA security force attempted to arrest the three Hamas men, who were hiding inside a building in the Shraim neighborhood south of Kalkilya. Gen. Adnan Damiri, spokesman for the PA security forces, said the Hamas men had immediately opened fire at the policemen, killing one and wounding another. Dozens of policemen who were rushed to the area surrounded the building and called on the Hamas gunmen - through loudspeakers and family members - to surrender or face death. In response, the Hamas men barricaded themselves inside the building, lobbing hand grenades and firing bullets from automatic rifles at the policemen, eyewitnesses said. Damiri expressed regret that the gunmen had rejected calls to end the standoff peacefully. He said that the Hamas-affiliated mayor of Kalkilya and former Hamas minister Omar Abdel Razek had also been recruited to persuade the three to surrender, but to no avail. "The Hamas leadership in the Gaza Strip has apparently instructed its men not to give themselves in to the Palestinian security forces," he said. He added that the three belonged to the same cell as the Hamas members killed on Sunday. The PA's newly-appointed interior minister, Said Abu Ali, said that his security forces wouldn't allow Hamas "outlaws" to tamper with the safety of the Palestinians or disrupt law and order. A senior PA security official accused Hamas of seeking to establish "military cells" in the West Bank with the hope of undermining the Palestinian security forces and overthrowing Abbas's administration. "Hamas wants to extend its control to the West Bank," he said. "They are investing a lot of money and weapons to achieve this goal. We are determined to foil their efforts." Hamas spokesman Fawzi Barhoum said that the Kalkilya incidents, as well as the stepped-up detention campaign against Hamas members in the West Bank, were not coincidental. He claimed that the clampdown was the result of Abbas's promise to US President Barack Obama, during their meeting in Washington last week, to implement the road map for peace and eliminate Hamas. Barhoum and other Hamas spokesmen said that their supporters in the West Bank would relate to Abbas's security forces from now on as if they were Israeli soldiers. He said Abbas's campaign against Hamas had destroyed any chance of resuming unity talks between the movement and Fatah in Cairo. The two parties were expected to meet in the Egyptian capital in early July in yet another attempt to form a unity government and end their bloody power struggle.