Israeli Prime Minister Benjamin Netanyahu has vowed to "respond with a heavy hand" after at least four people were killed and eight injured in what Israeli police described as a "terrorist" attack on a synagogue in Jerusalem.
Mr Netanyahu condemned Tuesday's violence as a "cruel murder of Jews who came to pray and were killed by despicable murderers”.
Palestinian President Mahmoud Abbas denounced the bloodshed in a statement, saying: "The presidency condemns the attack on Jewish worshippers in their place of prayer and condemns the killing of civilians no matter who is doing it."
A British-born man has been identified as one of the four killed in the attack.
Writing on Twitter, Israeli police spokesman Micky Rosenfeld said officers shot both suspects dead after they entered the synagogue in the ultra-Orthodox Har Nof neighbourhood armed with a meat cleaver and a pistol and attacked worshippers. An Israeli military spokesman posted a picture of a bloodied meat cleaver inside the building, apparently used in the killing spree.
Mr Rosenfeld said two police officers were among those injured in the attack, the deadliest to occur in Jerusalem for years.
Police said the attackers were Palestinians from East Jerusalem. The Popular Front for the Liberation of Palestine, a militant group, said the cousins were its members.
A PFLP statement did not specify whether the group instructed the cousins to carry out the attack. Hamas, the militant Palestinian group that runs the Gaza Strip, praised the attack.
The US Secretary of State John Kerry responded angrily to the attack and demanded that the Palestinian leadership take immediate steps to end incitement to violence.
Mr Kerry, who spoke before meeting in London with British Foreign Secretary Philip Hammond, said the violence witnessed on Tuesday "has no place anywhere".
"Innocent people who had come to worship died in the sanctuary of a synagogue. They were hatcheted, hacked and murdered in that holy place in an act of pure terror and senseless brutality and murder.
"I call on Palestinians at every single level of leadership to condemn this in the most powerful terms."
One man who was praying at the time of the attack told Israeli Channel 2 TV news: "I tried to escape. The man with the knife approached me. There was a chair and table between us ... my prayer shawl got caught. I left it there and escaped.”
In pictures: Jerusalem synagogue attack
In pictures: Jerusalem synagogue attack
Mourners attend the funerals of Aryeh Kupinsky, Cary William Levine, and Avraham Goldberg, three of the four people killed in a shooting attack in a synagogue in Jerusalem
A young mourner during the triple funeral of Rabbi Kalman Levine, Avraham Goldberg and Arieh Kupinsky
Ultra-Orthodox Jews mourn during a eulogy ceremony ahead of the funeral of Rabbi Moshe Twersky, one of the four jewish victims
Israeli Zaka emergency services volunteers carry the body of one of the two Palestinian assailants who were shot dead while attacking worshippers at a synagogue to an ambulance in the ultra-Orthodox Har Nof neighbourhood in Jerusalem
An Israeli man that was injured in an attack, by two Palestinians on Israeli worshippers at a synagogue, is taken to an ambulance by emergency personnel in the ultra-Orthodox Har Nof neighbourhood in Jerusalem
A bullet hole in the synagogue's front glass seen from inside and looking outwards to the Har Nof neighborhood in Jerusalem
An Israeli rescue worker navigates the scene of the shooting attack
Blood trails are seen on the floor near covered bodies at the scene of the attack on November 18, 2014
The bloody scene of the deadly attack
An Ultra-orthodox jewish man prays at the scene of an attack, by two Palestinians, on a synagogue in the ultra-Orthodox Har Nof neighbourhood in Jerusalem
Masked Palestinians hold axes and a gun as they celebrate with others an attack on a Jerusalem synagogue, in Rafah in the southern Gaza Strip
An Israeli police officer gestures as he holds a weapon near the scene of an attack at a Jerusalem synagogue
Blood trails are seen on the floor at the scene of an attack at a Jerusalem synagogue
Israeli emergency services personnel clean the sidewalk at the scene of an attack, by two Palestinians, on Israeli worshippers at a synagogue in the ultra-Orthodox Har Nof neighbourhood in Jerusalem
Israeli security forces stand next to the body of one of two Palestinian assailants who were shot dead while attacking a synagogue in the ultra-Orthodox Har Nof neighbourhood in Jerusalem
Israeli security personnel run next to the synagogue in Har Nof, where a suspected Palestinian attack took place
Israeli Zaka emergency services volunteers carry the body of an assailant who was shot dead while attacking a synagogue
Ultra-orthodox Jews watch the scene, after two Palestinians attacked a synagogue in the ultra-Orthodox Har Nof neighbourhood in Jerusalem
Israeli security forces secure the scene after two Palestinians attacked a synagogue in the ultra-Orthodox Har Nof neighbourhood in Jerusalem
Israeli security forces secure the scene, after two Palestinians attacked a synagogue in the ultra-Orthodox Har Nof neighbourhood in Jerusalem
Israeli TV footage showed the synagogue surrounded by police and rescue workers and the surrounding area cordoned off.
The violence comes amid high tensions in the city, with a wave of attacks killing at least six people in recent weeks.
Two weeks ago, a Palestinian driver was shot dead by Israeli police after ramming his car into a crowd at a tram stop in East Jerusalem, killing a border policeman and wounding 13 others.
A Palestinian bus driver was found hanging in his vehicle in a Jewish part of Jerusalem late Sunday, which was ruled a suicide by an inquest.
His relatives insisted that Yousef al-Ramouni, 32, was murdered because he was Arab.Reuse content