KIEV, Ukraine — European leaders are considering their toughest sanctions yet on Russian President Vladimir Putin as the U.S. says there’s evidence that Russia plans to supply rebels with heavy weapons including multiple rocket launchers.

With Ukraine and Russia trading accusations of shelling across each other’s borders, German Chancellor Angela Merkel is pushing European Union leaders to sign off on new sanctions next week. Merkel wants “to intensify the sanctions” and wants “quick decisions on this,” Georg Streiter, a German government spokesman, said yesterday. The Italian government, which chairs the EU Council, expects a deal on sanctions by next week, an EU official said.

“The shooting down of the airliner was a tipping point that’s changed the EU constellation,” Joerg Forbrig, senior program officer for central and eastern Europe at the Berlin bureau of the German Marshall Fund of the U.S., said in a phone interview. “Putin has crossed a line and misread the mood in European capitals to close ranks on new sanctions.”

On Saturday, Russia said that the United States bore some responsibility for the conflict in Ukraine though its backing for the Kiev government.

The drive by Merkel, who had so far taken a cautious approach to sanctions on Russia, shows how the downing of a Malaysian jet last week over east Ukraine is further isolating Putin in the international community. While he denies arming pro-Russian rebels, the U.S. says its intelligence shows that the missile that destroyed MH17, killing all 298 passengers and crew, was supplied by Russia.

European outrage has been fueled by the fact that MH17’s crash site still hasn’t been secured nine days after the disaster. The Netherlands, which lost 194 of its nationals on the flight, and Australia, have sent forensics experts to Ukraine and are considering deploying police at the site. Australia says some of its police will be armed.

The Dutch Safety Board may have a technical report with the first factual crash findings ready by the end of next week, Sara Vernooij, spokeswoman of the board, said by phone today.

The U.S. said there are signs Russia is planning to supply heavier weapons to rebels in east Ukraine.

“We have indications the Russians intend to move large- caliber weapons to the separatists,” U.S. Defense Department spokesman Steve Warren told reporters at the Pentagon Friday. Deliveries of arms such as multiple-launch rocket systems are “imminent” as part of a “continuing flow” of weapons to the pro-Russian rebels, he said. Russia’s Foreign Ministry said it had no comment on Warren’s statement.

Ukraine’s Defense Ministry said today that Russian forces shelled Ukrainian government positions six times overnight and that Russia continues sending troops and military vehicles across the border to aid the rebels. Ukrainian troops “liquidated” several sniper positions and have seized a large number of small arms, mortars, grenades and advanced Russian- made sniper rifles, the Defense Ministry said.

Four Ukrainian soldiers have been killed and 20 wounded in the past 24 hours, a Defense Ministry spokesman said. Nine civilians were killed and 29 were wounded in fighting in Luhansk over the past 24 hours, according to the city council’s website.

Ukrainian forces have advanced into the suburbs of Horlivka in the Donetsk region, the Defense Ministry said.

Rebel groups are increasingly in discord, especially the Vostok group and a group calling itself the Russian Orthodox Army, the Defense Ministry said.

The rebel stronghold of Donetsk, less than 60 miles from the border, awaits a possible onslaught by Ukrainian government forces.

The mayor of Kremenchuk, in central Ukraine, was shot dead by unknown assailants early today, the Interior Ministry said. Unknown attackers fired a grenade at the mayor’s house in the western city of Lviv last night, according to the city council’s website. There were no casualties.

The number of Russian troops on the border has risen to 12,000 from about 10,000, the Pentagon spokesman said.

The U.S. State Department first raised allegations of Russian cross-border fire two days ago. Russia rejected those accusations yesterday, with the Foreign Ministry saying in a statement that no evidence was provided to support the “false” claims because “it simply doesn’t exist.”

In turn, State Department spokeswoman Marie Harf told reporters in Washington yesterday that the U.S. has “seen no indications of Ukraine firing back into Russia.”

“The U.S. sanctions and the sanctions now being decided by the EU are going to have a strong impact on Russia’s economy,” Fredrik Erixon, director of the European Center for International Political Economy in Brussels, said in a phone interview. “An escalation of financial sanctions, not including trade sanctions, will shave 10 percent to 15 percent off the Russian economy in the next two to three years.”

Merkel is pushing EU leaders to sign off on measures against Russia by the end of next week and is prepared to accept curbs on her country’s technology exports to win support, according to two German government officials who asked not to be named because the discussions are private.

The European Commission, the 28-nation EU’s regulatory arm, will draw up detailed proposals for broader sanctions after getting the go-ahead from diplomats yesterday, commission spokeswoman Maja Kocijancic told reporters.

EU governments have already agreed to go beyond existing travel bans and asset freezes on individuals and companies deemed responsible for the unrest in Ukraine. The next wave may stop state-owned banks from financing themselves in Europe and prevent Russian companies buying high-tech equipment to develop energy resources, according to a document obtained yesterday by Bloomberg News.

Ukraine’s parliament will hold a special session of parliament on July 31 after the collapse of the ruling coalition and the resignation of Prime Minister Arseniy Yatsenyuk.

The move, announced late yesterday on President Petro Poroshenko’s website, came after Poroshenko, Yatsenyuk, the speaker of parliament, Oleksandr Turchynov and leaders of the parties in the legislature met to discuss how to carry on until a new coalition is formed.

Lawmakers plan to vote on two government-proposed bills, including one on funding the military and cutting social spending required under Ukraine’s $17 billion International Monetary Fund aid deal, that failed to gain approval before they went into a recess. They’ll also hold a vote of confidence in Yatsenyuk’s government.