Under the pretext of “strengthening Turkey’s security by clearing terrorist groups from the border and maintaining Syria’s territorial integrity,” the Turkish army launched a major escalation of the war in Syria on Wednesday with a cross-border operation codenamed Euphrates Shield.

Turkish units began their assault on ISIS and Kurdish militia forces at 4 AM local time, backed by tanks and supported by intensive artillery bombardments and airstrikes, including air support from the US-led coalition. The incursion marked the first time since last November, when Turkey shot down a Russian jet near the Turkish-Syrian border, that Turkish warplanes have struck inside Syria.

The invasion comes only days after a series of mortar shells targeted the Turkish town of Karkamis from the Syrian side of the border. Turkish authorities evacuated thousands of inhabitants.

There have also been a number of ISIS attacks in Turkey over the past two years, resulting in the deaths of hundreds of civilians. ISIS is the prime suspect in a deadly blast last Saturday at a wedding in the southeastern province of Gaziantep that left 54 people dead. After the suicide bombing, the Turkish government vowed to “completely clear the Turkish border” of terrorist elements.

Operation Euphrates Shield entails invading Syria and establishing a buffer zone, in blatant violation of Syrian sovereignty. This has long been advocated by the Turkish government and, at various times, by NATO allies. Democratic presidential candidate Hillary Clinton is calling for the imposition of a “safe zone” in Syria as a means of carving out a base of operations directed above all against the Russian- and Iranian-backed regime of President Bashar al-Assad.

Turkish Deputy Prime Minister Numan Kurtulmus had said earlier this week that proposals to establish a “secure zone,” an internationally policed buffer area, should be reconsidered.

The Turkish escalation will sharply increase tensions in an already unstable and explosive situation, with the United States, the major European powers, Iran, Russia and China all intervening to back competing factions in the Syrian war.

Once the invasion was underway it became clear that Washington was throwing its weight behind it. While the situation remains extremely fluid, it appears that the Obama administration, having undermined its relations with Turkey by tacitly backing the July 15 military coup against Turkish President Recep Tayyip Erdogan, is trying to rebuild its ties to Ankara at the expense of the Kurdish militias it has been supporting.

US Vice President Joseph Biden arrived in Ankara as the invasion of Syria was unfolding. After reiterating Washington’s claim, lacking all credibility, that it “did not have any foreknowledge” of the coup, he declared the US government’s support for Ankara’s invasion of Syria and endorsed its key aims.

At a press conference with Turkish Prime Minister Binali Yildirim, Biden insisted that Syrian Kurdish forces had to bow to Turkish demands and return to the eastern bank of the Euphrates River if they wanted to continue receiving US support. “We have made it absolutely clear that they must go back across the river. They cannot and will not, under any circumstances, get American support if they do not keep that commitment,” he said.

Russian officials, who had sought to develop closer ties with the Turkish regime in the aftermath of the abortive coup, indicated their concern over the military escalation. The Russian Foreign Ministry warned that Turkey’s air and ground operation could lead to “further degeneration of the situation in the conflict zone” and “flare-ups of interethnic tensions between Kurds and Arabs.”

Both the Assad regime and the Syrian Kurdish militias denounced the invasion. The Syrian Foreign Ministry said it “condemns the crossing of the Turkish-Syria border by Turkish tanks and armored vehicles towards the town of Jarabulus, with air cover from the US-led coalition, and considers it a flagrant violation of Syrian sovereignty.”

A Foreign Ministry source added, “Any party that wishes to fight terrorism on Syrian soil must coordinate with the Syrian government and army… What is happening in Jarabulus now is not a fight against terrorism. Rather, it is substituting one form of terrorism for another.”

The Kurdish militias, which have once again been double-crossed by their US imperialist backers, are providing yet one more example of the bankruptcy of their bourgeois nationalist orientation and their reliance on imperialism. Redur Xelil, spokesman for the People’s Protection Units (YPG), the Kurdish militia operating in Syria, complained that Turkey’s move was a “blatant aggression in Syrian internal affairs,” while Syrian Kurdish politician Aldar Xelil said the operation was a “declaration of war” on Kurdish autonomous administrations in northern Syria.

In an attempt to justify the incursion, Turkish authorities referred to United Nations resolutions calling for a fight against ISIS. They said Turkey was engaged in an act of “legitimate self-defense enshrined in the UN Charter.”

Turkish President Erdogan said, “Right now, unfortunately, all the attacks that happened in Gaziantep and Kilis…brought this issue to this point.” Referring to last Saturday’s Turkish security summit, Erdogan said Turkish officials had decided they “have to solve the problem.”

Speaking at a news conference in Ankara hours after the invasion, Turkish Foreign Minister Mevlut Cavusoglu said that the aim of the operation was to clear ISIS from the southern border. Turkish Interior Minister Efkan Ala underscored that the operation would continue until the “terror threat at our border is eliminated.”

Turkish authorities also insisted that Turkey was not invading Syria on its own, but operating in coordination with the US-led coalition and in support of the Free Syrian Army (FSA) fighters aiming to recapture the northern Syrian city of Jarabulus from ISIS.

However, the aim of the Turkish invasion is not limited to clearing ISIS from Jarabulus. Operation Euphrates Shield is a preemptive strike to block any attempt by Syrian Kurdish militias to capture Jarabulus before the Free Syrian Army (FSA) is able to take control. Making no distinction between ISIS and the YPG, Ankara has strengthened its FSA proxies against the Syrian Kurdish militias, the lead force within the so-called Syria Democratic Forces alliance (SDF) backed by the United States.

The growing influence in Syria of the Kurdish Democratic Union Party (PYD) and the crossing over to the western side of the Euphrates River of its military arm, the YPG, earlier this month alarmed Ankara, which fears the establishment of a US-backed autonomous Kurdish region in the Syrian-Turkish border region. Yesterday, following the onset of the invasion, Foreign Minister Cavusoglu called on Syrian Kurdish forces to go back to the eastern side of the Euphrates. “The US also supports this… I am saying very clearly that we will do what is necessary,” he said.

Last week, after Syrian war planes bombed US-backed Kurdish forces in the northern Syrian town of Hasakeh and Washington threatened to respond by attacking the Syrian regime, Turkey launched artillery barrages against both ISIS and Kurdish fighters near Jarabulus.

The opposition Republican People’s Party (CHP) and the far-right Nationalist Movement Party (MHP) are supporting the Turkish invasion. Speaking at a press conference following a Central Executive Board meeting, CHP spokeswoman and deputy chair Selin Sayek Boke expressed her party’s support for Operation Euphrates Shield, while criticizing the Justice and Development Party (AKP) government for waiting so long to attack ISIS both inside and outside of Turkey. The MHP is widely known as the leading advocate of an invasion of northern, Kurdish regions of Syria and Iraq.