Qatar has launched an investigation after Israel launched an attack in Doha targeting Hamas officials.

Condemning the 'cowardly' Israeli attack, Qatar said this attack is a flagrant violation of all international law and investigation ongoing on highest level.

Al Jazeera television, citing a Hamas source, said the attack targeted Hamas Gaza ceasefire negotiators. Several blasts were heard in Qatar's Doha on Tuesday, Reuters witnesses said.

Israel media, citing a senior Israeli official, said the attack was aimed at top Hamas leaders including Khalil al-Hayya, its Gaza chief.

Smoke was seen rising over the Katara District in the capital, an eyewitness said.