Kurdish fighters defending Kobane warn of a likely massacre by Islamic State insurgents, while Turkey says it will do whatever it can to prevent the Syrian border town from falling. (Reuters)

Islamic State fighters pounded the strategic Syrian border city of Kobane with artillery and tank fire Friday even as Turkey vowed to prevent the militants from capturing the embattled enclave.

In Iraq, government security forces planned a counteroffensive to reclaim the Euphrates River city of Hit after the Islamic State claimed control of the streets and hoisted its black flag. Jihadists also shot down a helicopter in northern Iraq on Friday, the Associated Press reported, quoting an official from Iraq’s Defense Ministry. The attack highlighted the Islamic State’s ability to take down aircraft as it threatens to seize more territory in both Syria and Iraq.

Both fronts are important tests of whether ground forces — backed by air power from a U.S.-led coalition — can gain the upper hand against well-armed Islamic State units seeking key territory.

Kobane would give the Islamic State control of a critical stretch of the Turkish-Syrian border, which could be used to expand clandestine supply routes. In Iraq, Hit represents another foothold in the Sunni heartland just 115 miles by road from Baghdad.

The battles also highlight the strength of the Islamic State firepower — mostly seized from Iraqi military sites — and the limitations of airstrikes that have concentrated on the militants’ oil smuggling and supply networks.

The United States has led a series of airstrikes in Syria. A look at the campaign thus far.

Kobane, defended by Syrian Kurdish militias, could be the first challenge for NATO-member Turkey after lawmakers in Ankara granted the military the right to conduct cross-border operations in Iraq and Syria. In addition, Turkey said it could allow foreign troops to use Turkish soil.

The vote Thursday paved the way for Turkey to play a more active role in the international coalition formed to confront the Islamic State, but Turkish officials cautioned that no immediate shift in Turkey’s position is likely.

Rather, the vote will be followed by negotiations between Ankara and Washington over the terms of Turkey’s participation in the coalition. A delegation of U.S. officials is due to visit Turkey next week.

Turkey has been reluctant to participate because it fears the U.S.-led air war in Syria will help shore up President Bashar al-Assad, whose continued hold on power Turkey regards as the root cause of the turmoil in Syria.

Turkey has not, however, ruled out unilateral action along its border to create buffer zones that would help protect civilians — a long-held Turkish ambition that has repeatedly been shunned by Washington. More than 160,000 Syrians have fled to Turkey as the Islamic State moved toward Kobane, adding to more than 1.5 million refugees in Turkey from Syria’s civil war.

Turkish Prime Minister Ahmet Davutoglu signaled that Turkey may be prepared to act to protect Kobane as Kurdish fighters braced for a full-fledged assault. Plumes of smoke rose after the bombardment by Islamic State fighters, who reached the outskirts of the town late Thursday.

“We wouldn’t want Kobane to fall. We’ll do whatever we can to prevent this from happening,” Davutoglu told journalists late Thursday night, according to comments quoted by Turkish media.

Syrian refugees chat near their tents in the Suruc district near Sanliurfa, southeast of Turkey. Turkey, according to the UN, is facing the 'biggest influx' of Syrian refugees since the start of the war three years ago. (Ulas Yunus Tosun/EPA)

“No other country has the capacity to affect the developments in Syria and Iraq. No other country will be affected like us either,” he said.

Possible Turkish intervention, however, has put Assad’s government in a difficult spot.

Assad views the Islamic State as another rising threat after battling rebel factions since 2011. On Friday, clashes between government forces and rebels occurred outside Aleppo, about 200 miles northwest of Damascus.

Hassoun Abu Faisal, a spokesman with the Aleppo Media Center, which monitors the conflict, said Syrian forces main some gains, but rebels tried to keep open key supply lines.

Assad’s government also strongly objects to Turkish military crossing into its territory. A statement from Syria’s Foreign Ministry described any possible Turkish incursion as “aggression” against the Assad government.

It is still not clear however how far Turkey is prepared to go to support the wider military effort against the Islamic State, which risks further complicating Turkey’s already tangled relationships with its own restive Kurdish population.

In Iraq, Islamic State militants tried to consolidate their hold on Hit after a fierce, day-long battle Thursday. The fighters seized a police compound and local government building, raising their black flags above the city, officials and residents said.

Iraqi police and army troops suffered heavy casualties and were forced to retreat, said Ahmed Saddak al-Dulaimi, chief of police in Anbar province, where Hit is located. Iraqi security forces backed by Sunni tribesmen were massing Friday outside Hit to retake the city, he said.

“There was street fighting all over Hit. There was fighting all night,” said Suleiman al-Kobaysi, a member of the Anbar provincial council. “The troops are just waiting for orders to reenter.”

Cunningham reported from Baghdad. Rebecca Collard in Beirut and Brian Murphy in Washington contributed to this report.