"We will study the detail of this agreement and discuss with colleagues in the EU and in the region," she said Thursday in a statement.
"On behalf of the EU, I am following the decision to form an interim Palestinian Government with great interest. The EU has consistently called for peace and reconciliation, under the authority of President Abbas, leading to an end to the division between the West Bank and Gaza and in support of greater security and stability across the region," the statement added.
Ending a bitter, and at times violent four-year rift, officials from the Islamist Hamas movement and the secular Fatah party of Palestinian Authority President Mahmoud Abbas signed the agreement in Cairo on Wednesday.
The deal provides for the establishment of an interim unity government.
A spokesman for Catherine Ashton would not be drawn on what reaction Hamas' inclusion in the Palestinian government would elicit from the EU.
Hamas, whose charter calls for the destruction of Israel, is considered as a terrorist group by the EU which refuses to deal with it because of its repeated refusal to heed demands to renounce violence, honour past Israeli-Palestinian peace agreements, and accept Israel's right to exist.
German Foreign Minister Guido Westerwelle said Thursday that no dialogue with Hamas was possible until it recognized Israel's right to exist.
'That's our guiding principle,' Westerwelle said, adding that Germany would consult with its allies about the Palestinian reconciliation.
Russia on the other hand, welcomed the deal, with a foreign ministry spokesman saying Moscow hoped the agreement would bring stability to the region.
'We have heard of this important step with great satisfaction,' the spokesman said.