The CSU's attack on the eurozone reform proposal came in a week already marked by a deep rift between the Bavarian party and Merkel over her liberal refugee policy that allowed more than a million asylum seekers to enter Germany since 2015.
She plans to meet leaders of countries including Italy and Greece at Sunday's mini-summit, which will be followed late next week by a full summit of the 28-nation EU. He mentioned Libya - the main jumping off point for countries bound for Europe - other African countries and the Balkans.
They met against the backdrop of heightened tension over migration.
Arriving at an emergency European Union mini-summit on migration, Italian Prime Minister Giuseppe Conte said he would put forward a "completely new proposal" for managing Europe's most divisive political issue.
Proactiva Open Arms, which has rescued thousands of migrants in the Mediterranean, said the Italians want the Libyan coast guard to conduct the rescues and return the migrants. No country has so far agreed to host any screening centers, according to the EU's top migration official.
A showdown over immigration between Merkel and her conservative CSU allies has escalated in the last week, but there were signs of a possible compromise when CSU chairman Horst Seehofer said on Sunday the row could be overcome.
Advisors to both leaders said they hadn't planned to spend much time on trade and U.S. president Donald Trump, having had their fill at the G-7 meeting in Quebec earlier this month.
"That is why there will be bilateral and trilateral agreements, how can we help each other - not always wait for all 28 members but think about what is important to whom", she said.
They said they were not briefed on the plan ahead of time and threatened not to back it.
Erdogan expects Turkey’s development level to reach the levels of Russia, US
If a candidate wins just over 50 percent of the vote, he will win the presidency, but if not, there will be a runoff on July 8. Supporters of Turkish President Tayyip Erdogan attend an election rally in Istanbul , Turkey, June 23, 2018.
More than 400 migrants were also rescued in three operations off the coast of Spain on Saturday, days after Madrid took in the more than 600 rejected by Italy and Malta.
Prime Minister Giuseppe Conte agreed to attend Sunday's meeting only after Merkel had assured him a draft leaders' statement prepared by the European Commission and circulated on Wednesday would be put aside.
"You can't have countries that massively benefit from the solidarity of the European Union and that massively voice their national selfishness when it comes to migrant issues", he told a press conference in Paris alongside new Spanish Prime Minister Pedro Sanchez.
Malta's home affairs minister, Michael Farrugia, and Italy's transport minister, Danilo Toninelli, engaged in a Twitter war of words Sunday over which country was being more "inhuman" about the fate of the Lifeline and its passengers.
But Maltese Prime Minister Joseph Muscat said the Lifeline "broke rules" by ignoring Italy's directions and should move towards its original destination "to prevent escalation".
Rome accused French President Emmanuel Macron on May 23 of "arrogance" for turning back migrants at the French-Italian border and minimizing Italy's problem.
Malta meanwhile has refused port to German aid group Mission Lifeline, which says it is carrying 234 migrants aboard its vessel and is now adrift in global waters.
Merkel is now on a Middle East tour that will also bring her to Lebanon later Thursday, where she is scheduled to meet Lebanese Prime Minister Saad Hariri.