Sunni militants say they have seized a strategically important border crossing and two towns along the Euphrates river in continued fighting in Iraq.
Officials admitted that the militants had seized the border crossing to Syria near the town of Qaim, killing 30 troops after a day-long battle.
Rebels also said they had taken the towns of Rawa and Aneh.
Correspondents say a campaign along the river may eventually lead to an assault on Baghdad from the west.
The capture of the Qaim crossing in western Iraq could help Isis transport weapons and other equipment to different battlefields, analysts say.
Sunni extremists have seized control of large areas of territory across Iraq in recent days.
They claim to have seized parts of Iraq's largest oil refinery, at Baiji, and have also taken a disused chemical weapons factory in Muthanna, 70km (45 miles) north-west of Baghdad.
On Saturday the government again denied that militants had gained access to parts of the Baiji refinery but did admit the army was facing 'violent attacks' from gunmen.
Analysis from the BBC's Jim Muir in Irbil
While keeping up the pressure on Baghdad from the north, where there is constant skirmishing in a belt roughly 70km (43 miles) from the capital, the militant Sunni rebels now seem to be preparing for a thrust from the west.
As well as taking the border crossing at Qaim, the rebels also say they have taken the nearby town of Qaim itself, as well as Rawa, about 70km to the east, the next stop on the Euphrates as it winds its way towards Baghdad.
South-east of Rawa, the town of Aneh also apparently fell to the militants without combat, and the Iraqi army's regional command HQ nearby is said to be surrounded.
Anbar province is heavily tribal, and the rebels say they are negotiating the handover of towns and villages without bloodshed in co-operation with local tribes.
Since January, they already control the town of Falluja, only 30km from Baghdad, and much of the regional capital Ramadi, about 40km further west.
The militants seem to be trying to connect up these two pockets and secure control of the whole Euphrates valley from the Syrian border to Baghdad.
Two government-held towns, Hit and Haditha, stand in their way along a 140km stretch of the river between Aneh and Ramadi.
If the rebels can join up those two areas and take full control in Ramadi, they would be in a position to prepare for an assault on the western approaches to Baghdad, using Falluja as the springboard.
Also on Saturday, thousands of Shia militia loyal to the powerful cleric Moqtada al-Sadr paraded through the streets of Baghdad.
The cleric, whose Mehdi Army fought the US in Iraq for years, had called for a military parade across the country.
Correspondents say the show of force will be seen as a very disturbing development by the Baghdad government.
The impressive-looking parade of men in battle fatigues accompanied by serious military hardware will only raise sectarian tensions at at time when the government is under pressure to rally the country together against the extremists, our correspondent reports.
US Secretary of State John Kerry is expected to travel to Iraq soon to press for a more representative cabinet, hoping this could ease tensions between the country's rival Muslim sects.
Iraq's sectarian split
Sunnis and Shia share fundamental beliefs, but differ in doctrine, ritual, law, theology and religious organisation The origins of the split lie in a dispute over who should have succeeded the Prophet Muhammad as leader of the Muslim community Sunnis are the majority sect in the Muslim world, but Shia, most of them ethnic Arabs, form between 60% and 65% of Iraq's population; Sunnis make up 32-37%, split between Arabs and Kurds Sunni Arabs dominated Iraq under Saddam Hussein and their persecution of the Shia stoked sectarian tensions; the US-led invasion in 2003 gave the Shia an opportunity to seek redress Nouri Maliki has been accused of denying Sunni Arabs meaningful representation and pursuing security policies that target them Sunnis and Shias: What's the story? Jeremy Bowen: Why Sunni-Shia tensions have returned Iraq crisis: Voices from Iraq
Meanwhile, US President Barack Obama said Isis - which has an estimated 10,000 fighters in Iraq and Syria - had exploited a power vacuum in Syria to amass arms and resources, but denied this was because the US had not moved to back moderate rebel forces fighting President Bashar Assad.
The US, which pulled out of Iraq in 2011, is sending some 300 military advisers to Iraq to help in the fight against the insurgents there.
But in the face of Iraqi calls for US air strikes, the White House is insisting that there is no purely military solution to the crisis.
Correspondents say Mr Obama believes Iraqi PM Nouri Maliki has endangered the country by ignoring Sunni concerns and governing in the interests of the Shia majority.
The UN estimates that about one million people have been displaced within Iraq as a result of violence this year.
About 500,000 people fled their homes in the country's second-largest city, Mosul, which Isis captured last week.
Isis in Iraq
Isis grew out of an al-Qaeda-linked organisation in Iraq
Estimated 10,000 fighters in Iraq and Syria Joined in its offensives by other Sunni militant groups, including Saddam-era officers and soldiers, and disaffected Sunni tribal fighters Exploits standoff between Iraqi government and the minority Sunni Arab community, which complains that Shia Prime Minister Nouri Maliki is monopolising power Isis led by Abu Bakr al-Baghdadi, an obscure figure regarded as a battlefield commander and tactician Jihadi groups around the world
Are you in Iraq or do you have family there? Have you been affected by recent events? You can send details of your experiences to haveyoursay@bbc.co.uk
using 'Iraq' in the subject line. Entities 0 Name: Iraq Count: 19 1 Name: Baghdad Count: 9 2 Name: US Count: 6 3 Name: Isis Count: 5 4 Name: Syria Count: 4 5 Name: Shia Count: 4 6 Name: Qaim Count: 4 7 Name: Iraqi Count: 3 8 Name: Ramadi Count: 3 9 Name: Rawa Count: 3 10 Name: Nouri Maliki Count: 3 11 Name: Baiji Count: 2 12 Name: west Count: 2 13 Name: Muslim Count: 2 14 Name: Falluja Count: 2 15 Name: White House Count: 1 16 Name: Moqtada al-Sadr Count: 1 17 Name: Bashar Assad Count: 1 18 Name: Iraq Isis Count: 1 19 Name: Jeremy Bowen Count: 1 20 Name: Euphrates Count: 1 21 Name: Abu Bakr al-Baghdadi Count: 1 22 Name: Euphrates river Count: 1 23 Name: Mehdi Army Count: 1 24 Name: Obama Count: 1 25 Name: Muthanna Count: 1 26 Name: Aneh Count: 1 27 Name: BBC Count: 1 28 Name: Jim Muir Count: 1 29 Name: Barack Obama Count: 1 30 Name: Irbil Count: 1 31 Name: Anbar Count: 1 32 Name: John Kerry Count: 1 33 Name: Saddam Hussein Count: 1 34 Name: Haditha Count: 1 35 Name: Muhammad Count: 1 36 Name: UN Count: 1 37 Name: Mosul Count: 1 Related 0 Url: http://ift.tt/1p3m7lQ Title: Dexter Filkins: The Crisis in Iraq Description: The events unfolding in Iraq point toward a much wider war, stretching from the Iranian frontier to the Mediterranean coast. The long open border between Iraq and Syria, and the big stretches of ungoverned space between them, has allowed extremists on each side to grow and to support one another.
