Kurdish and allied forces battling Islamic State militants have severed cross-border supply and communication lines between Iraq and Syria, according to the US-led coalition. The report comes after the IS suffered a series of defeats in both Iraq and Syria but have responded with retaliatory counteroffensives.

The news of the cross-border cut-off came as IS attacked Iraqi government military and security positions in the western Iraqi city of Ramadi with 17 car bombs, leaving at least 10 people dead, according to AFP.

The US-led Combined Joint Task Force announced that the two-week operation to cut IS supply routes was backed by coalition airstrikes and had "overcame ISIL [Islamic State] resistance" in and around the northeastern Syrian town of Tal Hamis in Hasakah Governate.

Kurdish forces backed by allied militias retook the strategically important town from Islamic State in late February. Fighting continued in the region, however, and the operation continued until March 7, according to a task force statement released Tuesday.

It added that Islamic State no longer enjoyed freedom of movement in the area and that the offensive had cut supply lines "historically used to move its personnel and materials into Iraq - namely Tal Afar and Mosul."

The coalition said fighters had seized "critical portions of Route 47 in Syria, a key ISIL communications and supply line leading into Iraq," the statement continued, noting 94 villages in the region were also retaken and that coalition airstrikes destroyed Islamic State weapons, vehicles and positions.

"This operation demonstrated the ability of anti-ISIL forces to further degrade Daesh [Islamic State] influence in this region," said task force commander Lt. Gen. James L. Terry. "The determination of these anti-ISIL forces and our precision airstrikes enabled us to deny Daesh this key terrain in Syria."

The majority of fighters battling Islamic State in the area are drawn from the Kurdish People's Protection Units (YPG).

"We are engaging in a very delicate battle because we are not facing fighters on the ground, we are facing booby-trapped terrain and sniper fire," an unnamed Iraqi major general told AFP from Tikrit. "Our movement is slow."

However, Islamic State launched a major offensive on a Kurdish-controlled border town on Wednesday, according to a monitoring group. Hundreds of militants along with tanks and heavy vehicles advanced on Ras al-Ayn, also in Hasakah province, leading to fierce fighting that left dozens dead on both sides, according to the UK-based Syrian Observatory for Human Rights.

Ras al-Ayn is the location of a border gate with the Turkish city of Ceylanpinar and is now controlled by Kurds, although in July 2013 the YPG battled hardline Syrian rebel groups for the town.

The Syrian Observatory for Human Rights, which gathers information from a network of local sources, reported that clashes were ongoing as of Wednesday.

Fighting also continued elsewhere in the area, the group said. It added that the YPG was now poised to re-capture villages near the Aleppo highway and in the countryside southeast of Kobani, another Kurdish-held border enclave. Kobani itself was the subject of a major Islamic State offensive last year which was only repelled with the help of heavy coalition airstrikes. The town became a rallying point for the fight against the jihadists and Syrian rebel groups and Iraqi peshmerga forces joined in its defence.

Meanwhile, in Iraq, pro-government forces are continuing to push the attack on Saddam Hussein's birthplace of Tikrit and have now entered the city itself, according to military sources.

An unnamed Iraqi major general who spoke with with AFP on Wednesday reported that troops, security forces and allied militias were now in control of the central military hospital and in the process of clearing the northern Qadisiyah neighbourhood as of Wednesday morning. However, he said that although Iraqi forces vastly outnumbered Islamic State fighters, his troops advance was slowed by the militants' use of guerrilla tactics.

"We are engaging in a very delicate battle because we are not facing fighters on the ground, we are facing booby-trapped terrain and sniper fire," he said. "Our movement is slow."

A 30,000-strong mixed force made up of Iraqi government troops and security forces alongside Shia militias and Sunni tribes backed by air power launched the assault on March 2. Commanders from regional Shia powerhouse Iran have also taken a leading role in the operation, a development described by the US military as "positive" but which has also raised concerns about the risk of increased sectarian tensions.

So far the attackers have advanced on towns to the north and south of Tikrit as well as from the east, partly encircling the city, but the IS fighters were understood to remain in control of the city itself.

Meanwhile, the synchronized IS car bomb attacks on Iraqi government forces positions in the Iraqi provincial capital of Ramadi, 60 miles west of Baghdad, were followed up with mortar rounds.

The attacks and subsequent clashes left at least 10 dead and 30 injured, according to police and hospital sources cited by AFP. Anbar's Governor Sohaib al-Rawi said 17 car bombs were involved and approximately 150 incoming mortar rounds fired, although other sources reported reported different numbers.

Ramadi is the capital of Anbar province, a majority of which, including neighbourhoods on the outskirts of the city, is controlled by Islamic State. However, the attack failed to make significant progress, Rawi said.

"Our brave security forces were ready & had excellent intelligence about the operation," the governor reported on his Twitter account. "Our security forces control the initiative. What happened in Ramadi today is a clear victory for Anbar"

We salute the security forces, our local police officers, the federal police & the sons of tribes. — Sohaib Alrawi (@Sohaib_Alrawi)March 11, 2015

The new Islamic State offensives may be an attempt to take the initiative after losing territory both in Iraq, where pro-government forces are moving north and Kurdish peshmerga fighters are reclaiming territory, and also in parts of Syria.

Wednesday's developments came ahead of an appearance by three of the US's top officials in front of Congress to discuss new military powers proposed by the Whitehouse to take on Islamic State.

Secretary of State John Kerry along with Joint Chiefs of Staff chair Gen. Martin Dempsey and Defense Secretary Ash Carter faced questions from the Senate Foreign Relations Committee on President Barack Obama plans for the use of increased military force against the group. The proposals were released in February and would permit the use of military force against Islamic State as well as a hypothetical "successor entity". Major ground operations of the kind seen in Afghanistan and post-invasion Iraq, however, would be ruled out.

They have proven somewhat controversial amongst lawmakers. Hawkish Republicans are likely to push for at least the option of a full-blown ground war, whereas some Democrats will wish to avoid that possibility in any form.