BRUSSELS (Reuters) - The European Union is poised to add new names to its list of Russians subject to sanctions over the coming days and will hold emergency talks on Monday, European Union sources said.

Leaders of the Group of Seven major economies agreed on Saturday to impose extra sanctions on Russia over its intervention in Ukraine, where armed pro-Moscow separatists detained a group of international observers and accused them of being Nato spies.

"The sanctions that will come on the European side in the next days will be the addition of new names to the list of individuals subject to asset freezes and a travel ban," a European Commission source said on condition of anonymity.

The European Union, whose nations have close trading and energy ties with Russia, has so far held out against imposing trade and financial sanctions.

But EU states have already agreed on names that could be quickly added to a list that so far stands at 33 people targeted by asset freezes and visa bans.

Senior EU diplomats will hold emergency talks in Brussels on Monday, EU sources said.