(CNN) -- Government troops backing Ivory Coast's President Laurent Gbagbo clashed with ex-rebels supporting the internationally recognized winner of last month's presidential vote Monday, as the European Union announced "targeted measures" aimed at Gbagbo's rule.
Alassane Ouattara's supporters attacked a checkpoint near the hotel that houses the former prime minister's office, surprising Gbagbo's forces and making off with a machine gun designed for mounting on a vehicle, witnesses reported. Gbagbo's troops responded to the raid by setting up a blockade of the hotel, barring all but a few diplomatic vehicles from passing.
Ouattara, a former economist for the International Monetary Fund who served as prime minister, was named the winner of a November presidential runoff by Ivory Coast's Independent Electoral Commission. But the country's Constitutional Council promptly invalidated those results and declared Gbagbo the winner.
Gbagbo has been sworn in for a new term, but several international organizations have called on him to step down and cede power to Ouattara.
Monday's skirmish was the first face-off between fighters led by Ouattara's prime minister, Guillaume Soro, and troops that remain loyal to Gbagbo since the post-electoral deadlock began. But efforts to resolve the impasse peacefully were still going on, with religious leaders meeting with Ouattara on Monday after sitting down with Gbagbo on Saturday.
Soro vowed Monday that he would install his administration by the end of the week -- but did not say how he would do that while penned into the Golf Hotel, nicknamed "The Republic of the Golf."
The former rebels have been working with U.N. peacekeepers to secure Ouattara's headquarters, which the head of Gbagbo's Republican Guard had threatened to "liberate" on Sunday. The country's military has remained loyal to Gbagbo despite pleas from Ouattara to join him.
The EU said Monday it plans to take "targeted measures" against people "who refuse to accept recent election results" in the Ivory Coast, an EU spokesman said Monday. Officials will settle on details of the "targeted measures" in the coming weeks, said the spokesman, who is customarily not named.
The 15-nation Economic Community of West African States has urged Gbagbo to "yield power without delay" and suspended the Ivory Coast from all of its decision-making bodies until further notice. And the African Union also has suspended the Ivory Coast "until such a time the democratically-elected president effectively assumes state power."
Gbagbo has accused Western officials of destabilizing his government by lobbying military leaders and state media to back his rival. His interior minister, Emile Guirieoulou, said in a televised address Saturday that Western military and civilian personnel stationed in the country "have undertaken to discretely and individually" try and persuade Ivory Coast generals to back Ouattara.
Observers say the threats of sanctions and financial isolation may be influencing Gbagbo. Young-Jin Choi, United Nations Secretary-General Ban Ki-moon's special envoy, met with Ouattara and said Gbagbo had agreed to meet with him.
Journalist Eric Agnero contributed to this report.